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The Collagen Triple Helix

The Collagen Triple Helix



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In the amino acid sequence X-Hyp-Gly (where X can be any amino acid) of the triple helix can the Hyp residue be both hydroxyproline and hydroxylysine? In our textbook it says that the Hyp residue is hydroxyproline but "hydroxylysine also occurs in the collagen".

Thank you!


The Collagen Triple Helix - Biology

The Triple Helix Structure of Collagen

I read the article The physicist and the dawn of the double helix with interest [see Karl Sigmund, Science, 366 (6461), 43 (4 October 2019)]. The physicists in the same era also contributed to the triple helix structure of the collagen.

The structure of DNA was decoded and published in 1953, revealing the double-helical shape but the structures of complex and even common proteins had then remained puzzling. On the suggestion of the renowned crystallographer John Desmond Bernal, the group of Gopalasamudram Narayanan Ramachandran in Chennai, India carried out the structural studies of collagen the most abundant protein among animals. Ramachandran used collagen from diverse sources (such as, shark fin, rat tail and kangaroo tail tendon) and showed that collagen has a ‘triple helix structure’ and published his results in a series of papers all with the direct title ‘Structure of Collagen’ (G. N. Ramachandran and G. Kartha, Nature 174 269–270 1954 G. N. Ramachandran and G. Kartha, Nature 176 593–595 1955 G. N. Ramachandran, Nature 177 710–711 1956 G. N. Ramachandran and V. Sasisekharan, Nature 190 1004–1005 1961). The ‘Ramachandran plot’ rank among the most outstanding contributions in structural biology, along with Pauling’s description of the α-helix and Watson and Crick’s discovery of the double helical structure of DNA (E. Subramanian, Nature Structural Biology 8 489–491 2001). The auditorium of the Central Leather Research Institute in Chennai is named as the ‘Triple Helix Auditorium’ in Ramachandran’s honour.


The Collagen Triple Helix - Biology

Opening Image: The triple helix of a collagen-like model peptide.

Outline

The collagen triple-helix and the a -helical coiled coil represent the two basic supercoiled protein motifs. The collagen triple-helix consists of a repeating Gly &ndashX&ndashY sequence. It is a major domain of all collagen proteins.

The Triple Helix
The Triple Helix
Backbone

A closer look at the backbone of the triple-helix (no side chain or hydrogen atoms). The chains are held together by noncovalent interactions (van der Waals forces, hydrophobic interactions, and hydrogen-bonds).

Every third residue passes through the center of the triple-helix, which is so crowded that only a Gly side chain can fit there.

The Triple Helix
Sidechains

Now all the backbone atoms are shown in spacefill. Zoom in .

The Triple Helix
Interchain Bonds

Zoom out to see the entire network of interchain hydrogen bonds.

The Triple Helix
Gly -15 to Ala Mutant
The Triple Helix
Gly -15 to Ala Mutant

Now for some recontructive surgery.

Finally , the complete backbone.

A Collagen Microfibril

Now we return to a spacefilling model of the wild-type collagen triple-helix. The resides are colored by group: Gly , Pro and Hyp .

Collagen functions by aggregating side-by-side into , which assemble into larger supramolecular arrays large enough to be seen in the electron microscope. Animate the assembly of a microfibril.


Technology

3Helix has developed a series of proprietary collagen hybridizing peptides that directly target the damaged collagen molecule. Collagen is the major component of nearly every human tissue, with an essential role in supporting cell growth and tissue formation. Damage to collagen is a strong indication of connective tissue injury, as well as a variety of diseases involving inflammation and abnormal tissue remodeling, such as cancer, myocardial infarction, arthritis, osteoporosis, and fibrosis. However, targeting damaged collagen is difficult with conventional technologies. In addition to providing CHP as a research tool for laboratory use in academia and industry, 3Helix is advancing its compounds to enable new pathways to achieving diagnostic and therapeutic objectives.

3Helix is based in Salt Lake City, Utah. It was founded by Drs. Yang Li and Michael Yu based on the technology that they invented at the Johns Hopkins University.

Founder Prof. Michael Yu describes examples of the vast potential medical applications of CHP, which was previously termed collagen mimetic peptide. (No access to Youtube? Watch the video here.)


Conclusions and perspectives

The triple helix is unique among all other protein structures – globular or fibrous – in its capacity to encode vast amounts of information that is available on its surface for utilization on the outside of cells (Fig. 5A). The triple helix, arranged in various patterns forming diverse supramolecular scaffolds, tethers and spatially organizes macromolecules, thus providing tensile strength to tissues and influencing cell behavior. This unique structure of the triple helix with its encoded degree of information evokes an analogy to the DNA double helix (Fig. 5A).

The fundamental importance of a triple helix in enabling animal multicellularity and tissue evolution. (A) The unique structure and vast encoding properties of the collagen triple helix outside the cell (left) evokes an analogy to the DNA double helix inside the cell (right). (B) The triple helix protein structure was present in unicellular organisms and was co-opted in the form of collagen IV, enabling the transition to multicellular animals. The triple helix was also adapted as a key feature of all members of the diverse collagen superfamily in the ECM, enabling tissue evolution. LCA, last common ancestor.

The fundamental importance of a triple helix in enabling animal multicellularity and tissue evolution. (A) The unique structure and vast encoding properties of the collagen triple helix outside the cell (left) evokes an analogy to the DNA double helix inside the cell (right). (B) The triple helix protein structure was present in unicellular organisms and was co-opted in the form of collagen IV, enabling the transition to multicellular animals. The triple helix was also adapted as a key feature of all members of the diverse collagen superfamily in the ECM, enabling tissue evolution. LCA, last common ancestor.

The biological importance of the triple helix is also evident from the almost 40 genetic diseases and its ubiquitous presence in animals. The triple helix was co-opted in the form of collagen IV to enable the evolutionary transition from unicellular organisms to multicellular animals, and the triple helix was also adapted to give rise to all the other members of the diverse collagen superfamily, thereby enabling the evolution of tissues and organs (Fig. 5B). Thus, the triple helix represents a fundamental protein structure that nature adapted for building an extracellular matrix.

There are many provocative and unanswered questions regarding the function of triple helices in suprastructures and their dysfunction in diseases. These include: (i) What are the unknown sites encoded in the triple helix for binding partners as exemplified by those in collagen I fibrils and collagen IV networks (Di Lullo et al., 2002 Parkin et al., 2011)? (ii) How is information in the triple helix used to assemble suprastructures (Orgel et al., 2011)? (iii) What are the mechanisms of how triple helices within suprastructures influence cell function? (iv) What is the impact of PTMs on the structure and function of the triple helix? (v) How do genetic mutations in the triple helix cause tissue dysfunction? (vi) How do genetic backgrounds affect phenotype variations? (vii) What are the mechanisms for the function of the triple helix in the transition from unicellular organisms to multicellular animals.

To answer such fundamental questions, collagen IV is an ideal archetype because it is the most ancient of the collagens, and it is present in unicellular organisms and non-bilaterian animals (Fig. 5B). Furthermore, recent studies have revealed that, in some organisms, collagen IV also occurs in the absence of a BM, such as in certain ctenophores and sponges, placozoans and the unicellular filasterean Ministeria vibrans (Fidler et al., 2017 Grau-Bove et al., 2017 Schierwater et al., 2009). Moreover, a recent study of Drosophila development provided evidence that, in the absence of BM, collagen IV has a role in intercellular adhesion and pro-growth signaling (Dai et al., 2017 Zajac and Horne-Badovinac, 2017). Together, these recent studies clearly indicate that collagen IV can have a direct role in influencing cell behavior, outside of the BM thus, the core functions of the collagen triple helix, as well as its role in the transition from unicellular organisms to multicellular animals, can be addressed by comparative studies in these organisms. Such knowledge may provide insights into unknown roles of collagens in cell biology, disease pathogenesis and evolution of animals.


The Collagen Triple Helix - Biology

a Institute of Chemistry, University of Manitoba, Dysart Rd. 144, Winnipeg, Manitoba, Canada
E-mail: [email protected]

Abstract

Collagen mimics are peptides designed to reproduce structural features of natural collagen. A triple helix is the first element in the hierarchy of collagen folding. It is an assembly of three parallel peptide chains stabilized by packing and interchain hydrogen bonds. In this review we summarize the existing chemical approaches towards stabilization of this structure including the most recent developments. Currently proposed methods include manipulation of the amino acid composition, application of unnatural amino acid analogues, stimuli-responsive modifications, chain tethering approaches, peptide amphiphiles, modifications that target interchain interactions and more. This ability to manipulate the triple helix as a supramolecular self-assembly contributes to our understanding of the collagen folding. It also provides essential information needed to design collagen-based biomaterials of the future.


Collagens at a glance

Collagens are a large family of triple helical proteins that are widespread throughout the body and are important for a broad range of functions, including tissue scaffolding, cell adhesion, cell migration, cancer, angiogenesis, tissue morphogenesis and tissue repair. Collagen is best known as the principal tensile element of vertebrate tissues such as tendon, cartilage, bone and skin, where it occurs in the extracellular matrix as elongated fibrils. Collagen is also well known for its location in basement membranes – for example, in the kidney glomerulus, where it functions in molecular filtration. However, the identification of transmembrane collagens on the surfaces of a wide variety of cells and collagens that are precursors of bioactive peptides that have paracrine functions has resulted in a revival of interest in collagen. Moreover, new developments in 3D reconstruction electron microscopy have led to new opportunities for studying intracellular trafficking of collagen. Newcomers to the field face the daunting task of sifting through 100,000 research papers that span 40 years. Here, we provide `the collagen basics'. Several excellent reviews are cited that are sources of more detailed descriptions and discussions.


50 years of collagen triple helix: a celebration of science

Abdul Kalam, President of India, at the podium. Sitting, left to right are T. Ramasami, S.P. Thyagarajan, R.N. Mashelkar, Kapil Sibal, V.S. Ramamurthy, and S.K.
Brahmachari.

G. N. Ramachandran (GNR) was an outstanding crystallographer and structural biologist. The model of collagen he developed has stood the test of time and has contributed greatly to understanding the role of this important fibrous protein. His pioneering contributions in crystallography, particularly in relation to methods of structure analysis using Fourier techniques and anomalous dispersion, are well recognized. The Ramachandran plot remains the simplest and most commonly used descriptor and tool for the validation of protein structures. He received many prizes, including the 1999 Ewald Prize of the IUCr.

Hia first major contribution to structural biology was the proposal, made along with Gopinath Kartha, of the triple helical structure of the fibrous protein collagen. The proposal was published in Nature in 1954. A symposium entitled '50 years of triple helix: a celebration of science' was organized by S.K. Brahmachari, M. Bansal, and T. Ramasami in New Delhi on August 7, 2004, to commemorate the 50th anniversary of this event. The symposium and and the production of a documentary on the life and work of GNR, were supported by the Council of Scientific and Industrial Research (CSIR) and the Dept. of Science & Technology (DST). R.A. Mashelkar, Director General of CSIR, gave the keynote address. Taking examples from his own research on polymers, he emphasized the importance of being alert to deal with unanticipated and unusual results. V.S. Ramamurthy, Secretary, DST, presided over the inaugural function.

Three of the speakers were former students of Ramachandran. M. Bansal, his last graduate student, worked on the role of hydroxyproline in collagen and traced the history of the discovery of the coiled coil triple helical structure of collagen. The way Ramachandran and Kartha, working in virtual isolation at the U. of Madras, conceptualized the collagen model using scanty biochemical and Xray data, was truly remarkable. Her own work led to the appreciation of water-mediated hydrogen bonds involving hydroxyproline.

C. Ramakrishnan, a co-architect of the Ramachandran plot, then described how the controversy regarding the so-called short inter-atomic distances in the collagen model structure, led to a thorough examination by the GNR group of the minimum permitted distances between different non-bonded atoms. From crystal structure data, they were found to be considerably less than the sums of the appropriate van der waals radii. This re-examination led to the Ramachandran plot which graphically illustrates the restrictions on polypeptide conformation. This was at a time when the structure of only one globular protein had been determined. Now, after forty years and thousands of structure determinations, the Ramachandran plot remains a very important tool for describing and validating protein structures.

A.S. Kolaskar, another student, discussed the contribution of Ramachandran to the development of computational biology and bioinformatics. His own work with GNR was concerned with the non-planarity of the peptide unit consequent to the pyramidal nature of the amide nitrogen. The non-planarity was established through quantum chemical calculations and analysis of crystal structure data.

M. Vijayan, former head of the Molecular Biophysics Unit (MBU) established by GNR at the Indian Inst. of Science, Bangalore, dealt with the GNR legacy in crystallography. He referred to GNR's contribution to the use of anomalous dispersion for structure analysis. Much of Ramachandran's contributions were theoretical or computational in nature. He was keen on initiating biological macromolecular crystallography in India, but it could not be done during his active professional life. However, he lived to see the MBU, one of the two schools he established, play a leadership role in the development of macromolecular crystallography in India.

The Central Leather Research Inst. (CLRI), Chennai (formerly Madras), is situated next to the laboratory in which GNR worked during the 1950s and the 1960s. The original sample of collagen used by GNR in his X-ray diffraction experiments was in fact supplied by CLRI. The current Director of CLRI, T. Ramasami, described this association as well as currently available collagenbased materials, particularly those developed at his own Institute. A large number of diseases associated with collagen malfunctioning have been identified. The presentation of D. Balasubramanian was concerned with these diseases while S.S. Sriramachari spoke on diseases related to the effect of dietary protein on collagen.

The last scientific session was related to genomics. H. Yang (Beijing Genomics Inst.) gave an overview of the activity in this area in China. He described how their progress from sequencing one percent of the human genome to 100 percent of the rice genome. The last talk was by S.K. Brhamachari, the main organizer of the meeting. He recalled his early experimental work pertaining to the hydroxylation of proline, as a graduate student of the MBU. He went on to discuss the major computational genomics and bioinformatics efforts, which are being pursued in conjunction with experimental studies, at his institution in Delhi.

A highlight of the symposium was the participation of the President of India, Abdul Kalam. Kalam made major contributions to Indian space and defense efforts before becoming the president. Kapil Sibal, the new Minister for Science and Technology, discussed the Indian government's commitment to scientific research and promised to remove the bureaucratic bottle necks that can get in the way of its meaningful pursuit. The President also interacted in a question-answer session with students.

Ramachandran's active research career in structural biology ended almost 25 years ago, well before his death in 2001, yet he remains a vibrant presence in the field. He was arguably the most outstanding scientist to have worked in independent India. He demonstrated how international science could be decisively influenced even when working under difficult conditions in less well-endowed neighbourhoods. The August 7 symposium was indeed a fitting tribute to his memory.


COLLAGEN RECEPTORS

Collagens are deposited in the extracellular matrix, but they participate in cell-matrix interactions via several receptor families (Heino et al. 2007, 2009 Humphries et al. 2006 Leitinger and Hohenester 2007). They are ligands of integrins, cell-adhesion receptors that lack intrinsic kinase activities. Collagens bind to integrins containing a β1 subunit combined with one of the four subunits containing an αA domain (α1, α2, α10, and α11) via GFOGER-like sequences, O being hydroxyproline (Humphries et al. 2006 Heino et al. 2007). There are other recognition sequences in collagens such as KGD in the ectodomain of collagen XVII, which is recognized by α5β1 and αvβ1 integrins but not by the “classical” collagen receptors (Heino et al. 2007). Several bioactive fragments resulting from the proteolytic cleavage of collagens are ligands of αvβ3, αvβ5, α3β1, and α5β1 integrins (Ricard-Blum and Ballut 2011).

Collagens I–III are also ligands of the dimeric discoidin receptors DDR1 and DDR2 that possess tyrosine kinase activities (Leitinger and Hohenester 2007). The major DDR2-binding site in collagens I–III is a GVMGFO motif (Heino et al. 2009). The crystal structure of a triple-helical collagen peptide bound to the discoidin domain (DS) of DDR2 has provided insight into the mechanism of DDR activation that may involve structural changes of DDR2 surface loops induced by collagen binding (Carafoli et al. 2009) (PDB ID: 2WUH). The activation may result from the simultaneous binding of both DS domains in the dimer to a single collagen triple helix, or DS domains may bind collagen independently (Carafoli et al. 2009). The soluble extracellular domains of DDR1 and DDR2 regulate collagen deposition in the extracellular matrix by inhibiting fibrillogenesis (Flynn et al. 2010). DDR2 affects mechanical properties of collagen I fibers by reducing their persistence length and their Young’s modulus (Sivakumar and Agarwal 2010).

Collagens bind to glycoprotein VI (GPVI), a member of the paired immunoglobulin-like receptor family, on platelets (Heino et al. 2007), and to the inhibitory leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1, Lebbink et al. 2006). Both receptors recognize the GPO motif in collagens. Ligands of LAIR-1 are fibrillar collagens I, II, and III, and membrane collagens XIII, XVII, and XXIII. Collagens I and III are functional ligands of LAIR-1 and inhibit immune cell activation in vitro. LAIR-1 binds multiple sites on collagens II and III (Lebbink et al. 2009). LAIR-1 and LAIR-2 are high affinity receptors for collagens I and III. They bind to them with higher affinity than GPVI (Lebbink et al. 2006, Lebbink et al. 2008), but three LAIR-1 amino acids central to collagen binding are conserved in GPVI (Brondijk et al. 2010). Fibril-forming collagens and collagen IV are also ligands of Endo180 (urokinase-type plasminogen activator associated protein), a member of the macrophage mannose-receptor family that mediates collagen internalization (Leitinger and Hohenester 2007 Heino et al. 2009). The identification of collagen sequences that bind to receptors has benefited from the Toolkits (overlapping synthetic trimeric peptides encompassing the entire triple-helical domain of human collagens II and III) developed by Farndale et al. (2008).


Introduction [ edit | edit source ]

Collagen is an essential part of the framework of the design of our various body tissues. is the major insoluble fibrous protein in the extracellular matrix and in connective tissue.

  • It is the single most abundant protein in the animal kingdom.
  • There are at least 16 types of collagen, but 80 – 90 percent of the collagen in the body consists of types I, II, and III
  • It is responsible for performing a variety of important biological functions.
  • It is most well-known for the structural role it plays in the body.
  • It is present in large quantities in connective tissue and provides bone, tendons and ligaments with tensile strength and skin with elasticity. It often works in conjuction with other important proteins such as keratin and elastin. [1][2]
  • Collagen production declines with age and exposure to factors such as smoking and UV light.
  • Collagen can be used in collagen dressings, to attract new skin cells to wound sites.
  • Cosmetic lotions that claim to increase collagen levels are unlikely to do so, as collagen molecules are too large to be absorbed through the skin [3] .

Function [ edit | edit source ]

Collagen is a hard, insoluble, and fibrous protein that makes up one-third of the protein in the human body.

  • In most collagens, the molecules are packed together to form long, thin fibrils. These act as supporting structures and anchor cells to each other. They give the skin strength and elasticity.
  • The collagens in the human body are strong and flexible.
  • Type 1 collagen fibrils are particularly capable of being stretched. Gram-for-gram, they are stronger than steel. [3]

There are close to 30 different types of collagen that have been identified so far. The most abundant type of collagen present in the human body is that of Type I with significant amounts of Type II,III and IV also accounted for.

  • Collagen I- found in bones, tendons, organs
  • Collagen II- found mainly in cartilage
  • Collagen III- found mainly in reticular fibres ( fine fibrous connective tissue occurring in networks to make up the supporting tissue of many organs).
  • Collagen IV- found in the basement membrane of cell membranes (a thin noncellular layer located between epithelial cells and the connective tissue that underlies them, composed of collagen and other proteins and having a variety of functions including support and filtration) [4]
  • Collagen V- found in hair, nails [2]

Collagen Synthesis and structure [ edit | edit source ]

  1. The production of collagen starts with procollagen—the substance secreted by your cells. It goes through processing in two parts of your cell, the endoplasmic reticulum and Golgi body.
  2. This whole process needs vitamin C.
  3. The structure of a collagen protein is what gives it the unique strength your body needs. It’s a triple helix—three chains twisting around each other.
  4. There are 1,050 amino acids in each of the three chains that make up collagen. And they’re held together with hydrogens—the smallest atom.
  5. Glycine is amino acid that takes up the middle of the triple helix structure because it’s the only one that can fit. Glycine is an amino acid that has a single hydrogen atom as its side chain. It is the simplest amino acid.
  6. These long fibers don’t just exist as single protein ropes. Collagen can come together to form striated horizontal sheets. [5]

NB The older you get, the less collagen you make. And what you do make is not as high-quality as the collagen of your youth. This impacts the appearance of skin, the maintenance of joint health, and much more. [5]


The Collagen Triple Helix - Biology

Electron Microscope Observation of Collagen fibers

The Institute of Optics, University of Rochester

Spring 2006 Final Project

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 40% of the total. It is one of the long, fibrous structural proteins whose structure and functions are quite different from those of globular proteins such as enzymes.

Fig 1. Collagen triple helix

Collagen is distinct from other proteins in that the molecule comprises three polypeptide chains which form a unique triple-helical structure (See figure 1). It is tough and inextensible, with great tensile strength, and is the main component of cartilage, ligaments and tendons, and the main protein component of bone and teeth. Along with soft keratin, it is responsible for skin strength and elasticity, and its degradation leads to wrinkles that accompany aging. It strengthens blood vessels and plays a role in tissue development. It is present in the cornea and lens of the eye in crystalline form.

More than 20 types of collagen are known up to now, different types are determined by different polypeptide sequences. Their properties are different and they can be found in different places of animal body.

Samples used in this project including a rat cornea sample for SEM imaging collagen type I fibrils, a bovine collagen type III solution sample (Rockland Immunochemicals Inc. 1× PBS diluted to 0.1mg/ml) for TEM studying collagen type III fibrils and an insoluable bovine collagen type I fiber sample( Sigma Aldrich) for microscope observation.

The rat cornea sample used for SEM imaging was HMDS dehydrated, the fixing and dehydration process is as follows:

1) Immerse freshly cut tissue sample in physiological saline

2) Transfer the sample to a solution containing 1% Glutaraldehyde in 0.1M Cacodylate buffer, PH 7.

Allow 5 minutes for sample fixing process.

3) Wash in distilled water for 5 minutes

4) Dehydrate using a series of ethanol washes:

50% ethanol 5 minutes 75% ethanol 5 minutes 90% ethanol 5 minutes 100% ethanol 5 minutes.

5) Immerse in HMDS for 15 minutes and air dried in room temperature in fume hood.

We then mounted the sample on the SEM sample stub and sputtered a layer of gold on it in a sputter coater.

After that the sample was well grounded with the conductive paint, and was ready for SEM imaging.

To improve contrast of our TEM images, we used the negative staining technique.

For our collagen type III sample we used 1% phosphotungstic acid as our negative stain.

The stain process is as follow:

1) A drop of collagen solution is placed on a petri dish.

2) A carbon coated EM grid (Fig 2) is placed carbon side down on top of the collagen solution drop for approximately 1-3 minutes.

3) The grid is removed, blotted with filter paper and placed onto a drop of stain solution, for one minute.

4) Then remove the excess stain solution.



Light microscope sample preparation

For light microscope samples, we don't need special sample preparation process. We simply put a piece of collagen fiber sample on a microscope slide, covered it with a coverslip and then put the sample under the microscope objective to observe.

Different samples should be imaged by different imaging techniques. For bulk and nontransparent samples like the rat cornea sample we use SEM. For thin and transparent sample like the collagen type III solution sample we use TEM. For prior electron microscopy observation that doesn't need large magnifications, we use light microscope .

Fig 3 is an SEM image we got from the rat cornea sample at 10000 × magnification. We can see, in this picture, some big bundles of collagen fibrils lying around. Also, we can clearly see the fine fabrics of single collagen fibrils which make up the whole rat cornea .

Fig.3 Rat Cornea SEM image 10000 ×

We then took a closer look at a small area at 50000 × magnification. Here we can clearly see single fibrils in the background, which are about 20nm in diameter in average. There is a big bundle of fibrils lying above the collagen fibril fabrics background. We can even almost see how single collagen fibrils twisted with each other to form the fibril bundle. The left image in figure is the original image and the right one is a colorized image.

Fig.4 Rat Cornea SEM image 50000 ×

Figure 5 and figure 6 are TEM images we got from the PBS buffered 0.1mg/ml bovine collagen type III solution sample. The contrast of these images are good because of the negative stain: 1% phosphotungstic acid we used in the experiment. The magnification is 125000 × , and we can clearly see the big mess of the collagen type III fibrils. The fibrils are also about 20 nm in diameter. The left images in these figures are the original TEM images and the right ones are the colorized version. We can see the collagen type III fibrils in the solution form a gel and exhibit complicated 3D structure.

Fig 5. Bovine collagen type III solution TEM image 125000 ×

Fig 6. Bovine collagen type III solution TEM image 125000 ×

Figure 7 is the light microscope image of the insoluable bovine collagen type I fiber sample .

Fig 7. Bovine collagen type I fiber sample light microscope 100 ×

Light microscopy, SEM, TEM, sample fixing and dehydration for SEM, sample sputter coating for SEM, negative staining for TEM, image colorization.

Luckily the SEM and TEM images all looks good. We successfully observed different collagen types by different electron microscopy techniques and the images all look like what they are expected to be. The collagen type I fibrils in rat cornea form into a fine fabrics or twisted together into a big bundle. The collagen fibrils in the bovine collagen type III solution form into a collagen gel with complicated 3D structure. This project is very helpful for a better understanding on collagen structures and properties, and for a better knowledge on SEM, TEM and light microscope imaging techniques as well.

Thanks Brian for his help and guidance. Thanks Ms. Karen for generous donation of 1% phosphotungstic acid negative stain . Thanks Dr. Edward Brown for cutting rat cornea and his guidence.

1) Kadler et al, Collagen fibril formation, Biochem. J. (1996) 316, 1-11


Watch the video: USMLE Step 1 - Lesson 22 - Collagen: Types, Structure, and Synthesis (August 2022).