Segment-long-spacing crystallites, a powerful tool in collagen research

Collagen Mimetic Peptide with a Coiled Coil Trimerization Domain Forms Fibrils Having D-Period-like Structures

Fibrillar collagen is the major protein in the extracellular matrix and regulates cell behavior via chemical and mechanical cues. The key structural element of collagen fibrils is the axially repeating D-period, formed by the lateral association of collagen triple helices. We have developed fibril-forming collagen mimetic peptides (FCMPs) with repeated amino acid sequences, which form fibrils having D-period-like structures. Containing over 100 amino acid residues, these peptides are produced by bacterial expression using designed genes. Here, we report the fibrillogenesis of a new FCMP containing an α-helix coiled coil domain. The latest findings highlight the importance of the amino acid sequence periodicity in FCMP fibril formation. Additionally, our results demonstrate the remarkable adaptability of collagen fibrils' molecular packing. Mirroring native collagen fibrils, in both the structure and the fibrillogenesis process, these FCMPs are useful molecular tools for advancing collagen research and developing novel biomaterials.

Assessing Collagen D-Band Periodicity with Atomic Force Microscopy

The collagen superfamily includes more than fifty collagen and/or collagen-like proteins with fibril-forming collagen type I being the most abundant protein within the extracellular matrix. Collagen type I plays a crucial role in a variety of functions, it has been associated with many pathological conditions and it is widely used due to its unique properties. One unique nano-scale characteristic of natural occurring collagen type I fibers is the so-called D-band periodicity, which has been associated with collagen natural structure and properties, while it seems to play a crucial role in the interactions between cells and collagen and in various pathological conditions. An accurate characterization of the surface and structure of collagen fibers, including D-band periodicity, on collagen-based tissues and/or (nano-)biomaterials can be achieved by Atomic Force Microscopy (AFM). AFM is a scanning probe microscope and is among the few techniques that can assess D-band periodicity. This review covers issues related to collagen and collagen D-band periodicity and the use of AFM for studying them. Through a systematic search in databases (PubMed and Scopus) relevant articles were identified. The study of these articles demonstrated that AFM can offer novel information concerning D-band periodicity. This study highlights the importance of studying collagen D-band periodicity and proves that AFM is a powerful tool for investigating a number of different properties related to collagen D-band periodicity.

Segment-Long-Spacing (SLS) and the Polymorphic Structures of Fibrillar Collagen

The diverse and complex functions of collagen during the development of an organism are closely related to the polymorphism of its supramolecular structures in the extracellular matrix. SLS (segment-long-spacing) is one of the best understood alternative structures of collagen. SLS played an instrumental role in the original studies of collagen more than half a century ago that laid the foundation of nearly everything we know about collagen today. Despite being used mostly under in vitro conditions, the natural occurrence of SLS in tissues has also been reported. Here we will provide a brief overview of the major findings of the SLS and other structures of collagen based on a wealth of work published starting from the 1940s. We will discuss the factors that determine the stability and the structural specificity of the different molecular assemblies of collagen in light of the new studies using designed fibril forming collagen peptides. At the end of the chapter, we will summarize some recent discoveries of the alternative structures of collagen in tissues, especially those involved in pathogenic states. A revisit of SLS will likely inspire new understandings concerning the range of critical roles of fibrillar collagen in terms of its organizational diversity in the extracellular matrix.

The collagen type I segment long spacing (SLS) and fibrillar forms: Formation by ATP and sulphonated diazo dyes

The collagen type I segment long spacing (SLS) crystallite is a well-ordered rod-like molecular aggregate, ∼300nm in length, which is produced in vitro under mildly acidic conditions (pH 2.5-3.5) in the presence of 1mM ATP. The formation of the SLS crystallite amplifies the inherent linear structural features of individual collagen heterotrimers, due to the punctate linear distribution and summation of the bulkier amino acid side chains along the length of individual collagen heterotrimers. This can be correlated structurally with the 67nm D-banded collagen fibril that is found in vivo, and formed in vitro. Although first described many years ago, the range of conditions required for ATP-induced SLS crystallite formation from acid-soluble collagen have not been explored extensively. Consequently, we have addressed biochemical parameters such as the ATP concentration, pH, speed of formation and stability so as to provide a more complete structural understanding of the SLS crystallite. Treatment of collagen type I with 1mM ATP at neutral and higher pH (6.0-9.0) also induced the formation of D-banded fibrils. Contrary to previous studies, we have shown that the polysulphonated diazo dyes Direct red (Sirius red) and Evans blue, but not Congo red and Methyl blue, can also induce the formation of SLS-like aggregates of collagen, but under markedly different ionic conditions to those employed in the presence of ATP. Specifically, pre-formed D-banded collagen fibrils, prepared in a higher than the usual physiological NaCl concentration (e.g. 500mM NaCl, 20mM Tris-HCl pH7.4 or x3 PBS), readily form SLS aggregates when treated with 0.1mM Direct red and Evans blue, but this did not occur at lower NaCl concentrations. These new data are discussed in relation to the anion (Cl(-)) and polyanion (phosphate and sulphonate) binding by the collagen heterotrimer and their likely role in collagen fibrillogenesis and SLS formation.

Self-association of streptococcus pyogenes collagen-like constructs into higher order structures

A number of bacterial collagen-like proteins with Gly as every third residue and a high Pro content have been observed to form stable triple-helical structures despite the absence of hydroxyproline (Hyp). Here, the high yield cold-shock expression system is used to obtain purified recombinant collagen-like protein (V-CL) from Streptococcus pyogenes containing an N-terminal globular domain V followed by the collagen triple-helix domain CL and the modified construct with two tandem collagen domains V-CL-CL. Both constructs and their isolated collagenous domains form stable triple-helices characterized by very sharp thermal transitions at 35-37 degrees C and by high values of calorimetric enthalpy. Procedures for the formation of collagen SLS crystallites lead to parallel arrays of in register V-CL-CL molecules, as well as centrosymmetric arrays of dimers joined at their globular domains. At neutral pH and high concentrations, the bacterial constructs all show a tendency towards aggregation. The isolated collagen domains, CL and CL-CL, form units of diameter 4-5 nm which bundle together and twist to make larger fibrillar structures. Thus, although this S. pyogenes collagen-like protein is a cell surface protein with no indication of participation in higher order structure, the triple-helix domain has the potential of forming fibrillar structures even in the absence of hydroxyproline. The formation of fibrils suggests bacterial collagen proteins may be useful for biomaterials and tissue engineering applications.

Potential modifier role of the R618Q variant of proalpha2(I)collagen in type I collagen fibrillogenesis: in vitro assembly analysis

An arginine to glutamine substitution in the triple helix of proalpha2(I)collagen (R618Q) was first reported in a patient with a variant of Marfan syndrome and later identified in conjunction with a second mutation in a patient with osteogenesis imperfecta (OI). The presence of the R618Q proalpha2(I)collagen allele in unaffected or mildly affected family members suggests that the R618Q allele is either a non-affecting polymorphism or a potential genetic modifier. Conservation of arginine618 across species and fibrillar collagen types suggests it is functionally significant. To investigate the functional significance of the R618Q proalpha2(I)collagen allele, we isolated type I collagen from cultured dermal fibroblasts of control and two unrelated individuals heterozygous for the R618Q proalpha2(I)collagen allele and evaluated helical stability and fibrillar assembly. Type I collagen thermal stability analyzed by protease susceptibility and CD spectroscopy demonstrated no statistical difference between control and R618Q containing collagen molecules. In vitro fibril assembly analyses demonstrated that R618Q containing collagen exhibits rapid fibrillar growth with minimal fibril nucleation phase. Further, electron microscopy demonstrated that the diameter of assembled R618Q containing collagen fibrils was approximately 20% of control collagen fibrils. These findings suggest the R618Q variant does not impact triple helical stability but has a role in collagen fibril assembly, supporting the hypothesis that the R618Q proalpha2(I)collagen variant is a modifier of connective tissue structure/function and is potentially involved in disease pathogenesis.

Hierarchical assembly and the onset of banding in fibrous long spacing collagen revealed by atomic force microscopy

The mechanism of formation of fibrillar collagen with a banding periodicity much greater than the 67 nm of native collagen, i.e. the so-called fibrous long spacing (FLS) collagen, has been speculated upon, but has not been previously studied experimentally from a detailed structural perspective. In vitro, such fibrils, with banding periodicity of approximately 270 nm, may be produced by dialysis of an acidic solution of type I collagen and alpha(1)-acid glycoprotein against deionized water. FLS collagen assembly was investigated by visualization of assembly intermediates that were formed during the course of dialysis using atomic force microscopy. Below pH 4, thin, curly nonbanded fibrils were formed. When the dialysis solution reached approximately pH 4, thin, filamentous structures that showed protrusions spaced at approximately 270 nm were seen. As the pH increased, these protofibrils appeared to associate loosely into larger fibrils with clear approximately 270 nm banding which increased in diameter and compactness, such that by approximately pH 4.6, mature FLS collagen fibrils begin to be observed with increasing frequency. These results suggest that there are aspects of a stepwise process in the formation of FLS collagen, and that the banding pattern arises quite early and very specifically in this process. It is proposed that typical 4D-period staggered microfibril subunits assemble laterally with minimal stagger between adjacent fibrils. alpha(1)-Acid glycoprotein presumably promotes this otherwise abnormal lateral assembly over native-type self-assembly. Cocoon-like fibrils, which are hundreds of nanometers in diameter and 10-20 microm in length, were found to coexist with mature FLS fibrils.

Investigating the ultrastructure of fibrous long spacing collagen by parallel atomic force and transmission electron microscopy

The ultrastructure of fibrous long spacing (FLS) collagen fibrils has been investigated by performing both atomic force microscopy (AFM) and transmission electron microscopy (TEM) on exactly the same area of FLS collagen fibril samples. These FLS collagen fibrils were formed in vitro from type I collagen and alpha1-acid glycoprotein (AAG) solutions. On the basis of the correlated AFM and TEM images obtained before and after negative staining, the periodic dark bands observed in TEM images along the longitudinal axis of the FLS collagen fibril correspond directly to periodic protrusions seen by AFM. This observation is in agreement with the original surmise made by Gross, Highberger, and Schmitt (Gross J, Highberger JH, Schmitt FO, Proc Natl Acad Sci USA 1954;40:679-688) that the major repeating dark bands of FLS collagen fibrils observed under TEM are thick relative to the interband region. Although these results do not refute the idea of negative stain penetration into gap regions proposed by Hodge and Petruska (Petruska JA, Hodge AJ. Aspects of protein structure. Ramachandran GN, editor. New York: Academic Press; 1963. p. 289-300), there is no need to invoke the presence of gap regions to explain the periodic dark bands observed in TEM images of FLS collagen fibrils.

Ultrastructure and assembly of segmental long spacing collagen studied by atomic force microscopy

The in vitro formation of segmental long spacing (SLS) collagen as induced by the addition of ATP to acidified Type I collagen solutions has been examined with the atomic force microscope (AFM). AFM images obtained suggest that the assembly proceeds in a stepwise manner, through an intermediate stage of oligomers, which then associate laterally to form the so-called "SLS crystallites". Attempts to induce SLS formation by the addition of other polyanionic species to monomeric collagen solutions met with mixed success; ATP-gamma-S and GTP produced SLS crystallites, whereas inorganic phosphate and other polyanionic dyes did not. This indicates that the formation of SLS cannot simply be attributed to the negation of positive charges believed to be located on the end of the collagen monomer, but rather it is a complex function of the structure and charge of both the collagen monomer and polyanion.

A model for type II collagen fibrils: distinctive D-band patterns in native and reconstituted fibrils compared with sequence data for helix and telopeptide domains

The periodical D-band pattern is generally considered a unique ultrastructural feature shared by all fibril-forming collagens, which correlates with the intrafibril, paracrystalline array of tropocollagen monomers. Distinct band patterns have been reported, however, for collagen stained long-spacing (SLS) crystallites of genetic types I, II, and III. Moreover, D-band patterns of negatively stained, native type II collagen fibrils were found to be not identical to those of type I in our previous research. Because of (a) these distinctive features, (b) tropocollagen heterotrimeric conditions (type I) vs homotrimeric conditions (type II), and (c) different lengths and poor homology between extrahelical telopeptides, the molecular array or telopeptide conformation within the extensively studied type I collagen fibrils could be not the same as those in the very much less intensively studied type II collagen fibrils. In this investigation, a distinctive positive-staining D-band pattern was found for type II collagen fibrils obtained from human cartilages. A fibril model was developed by analyzing actual D-band patterns, and matching them against simulated patterns based on the primary structure of extrahelical and helical domains in human type II tropocollagen. In particular, a more prominent b(1) band was apparent in native type II collagen fibrils than in type I. This distinctive feature was also observed for native-type collagen fibrils reconstituted from purified type II collagen, i.e., free from associated minor type XI collagen. On modeling possible monomer arrays, the best fit between microdensitograms and simulation traces was found for 234 amino acid staggering, as is also the case for type I collagen fibrils. On comparing this model with an analogous one for type I collagen fibrils, there was a higher intraband distribution of charged residues for band b(1), consistent with the higher electrondensity observed for this band in type II collagen fibrils. N- and C-telopeptide displacement in the model corresponded to D-locations of a c(2) subband, which we named c(2.0), and band a(3), respectively. In simulation profiles, c(2.0) -like and a(3) -like peaks mimicked the corresponding peaks in microdensitograms when molecular reversals were adopted at positions 10N-12N, 12C-14C, and 17C-19C for N- and C-telopeptides. Hydrophobic interactions and algorithmic predictions of protein secondary structure, according to Chou and Fasman and Rost and Sander criteria, were consistent with these conformational models, and suggest that an additional molecular reversal may occur at positions 3N-5N. These telopeptide "S-fold" conformations, interpreted as axial projections of tridimensional conformation, may represent starting points for further investigation into the still unresolved tridimensional conformation of telopeptides in monomers arrayed within type II collagen fibrils.

Fourier analysis of electron micrographs of positively stained collagen fibrils: application to type I and II collagen typing

Type I and II collagen (native-type) fibrils, positively stained with uranyl acetate, present typical periodic (D = 67 nm) cross-striation patterns. Although the two patterns are similar, the distributions of charged amino acids along the type I and II collagen molecules are different. After optical diffraction analysis or computer image processing of electron micrographs, different Fourier transforms were obtained from type I and II collagen fibrils, either as native fibrils or after in vitro reconstitution from purified molecules. With tissues such as tendon and cartilage, better results were obtained after mild trypsin treatment, which allowed better isolation and staining of the collagen fibrils. The main difference observed in the Fourier transforms was the presence in type II collagen fibrils of a strong tenth-order peak (corresponding to the tenth harmonic of the fundamental frequency). In order to discriminate between the two collagens, we measured the ratio (R) of the areas under the ninth- and tenth-order peaks. In trypsin treated tissues, the distributions of these ratios were clearly separated: below 1.0 for type II collagen fibrils and above 1.5 for type I collagen fibrils. This method appears to be suitable for rapid typing of type I and II collagen fibrils and might be useful for determining the exact composition of fibrils in tissues, such as intervertebral discs, that contain these both types of collagen.

Basement-membrane stromal relationships: interactions between collagen fibrils and the lamina densa

Collagens, the most abundant molecules in the extracellular space, predominantly form either fibrillar or sheet-like structures-the two major supramolecular conformations that maintain tissue integrity. In connective tissues, other than cartilage, collagen fibrils are mainly composed of collagens I, III, and V at different molecular ratios, exhibiting a D-periodic banding pattern, with diameters ranging from 30 to 150 nm, that can form a coarse network in the extracellular matrix in comparison with a fine meshwork of lamina densa. The lamina densa represents a stable sheet-like meshwork composed of collagen IV, laminin, nidogen, and perlecan compartmentalizing tissue from one another. We hypothesize that the interactions between collagen fibrils and the lamina densa are crucial for maintaining tissue-tissue interactions. A detailed analysis of these interactions forms the basis of this review article. Here, we demonstrate that there is a direct connection between collagen fibrils and the lamina densa and propose that collagen V may play a crucial role in this connection. Collagen V might also be involved in regulation of collagen fibril diameter and anchoring of epithelia to underlying connective tissues.

The evolution of fibrillar collagens: a sea-pen collagen shares common features with vertebrate type V collagen

The extracellular matrix of marine primitive invertebrates (sponges, polyps and jellyfishes) contains collagen fibrils with narrow diameters. From various data, it has been hypothesized that these primitive collagens could represent ancestral forms of the vertebrate minor collagens, i.e., types V or XI. Recently we have isolated a primitive collagen from the soft tissues of the sea-pen Veretillum cynomorium. This report examines whether the sea-pen collagen shares some features with vertebrate type V collagen. Rotary shadowed images of acid-soluble collagen molecules extracted from beta-APN treated animals, positive staining of segment-long-spacing crystallites precipitated from pepsinized collagen, Western blots of the pepsinized alpha1 and alpha2 chains with antibodies to vertebrate types I, III and V collagens, and in situ gold immunolabeling of ECM collagen fibrils were examined. Our results showed that the tissue form of the sea-pen collagen is a 340-nm threadlike molecule, which is close to the vertebrate type V collagen with its voluminous terminal globular domain, the distribution of most of its polar amino-acid residues, and its antigenic properties.

Effects of thyro-parathyroidectomy and parathyroidectomy upon dentinogenesis: Part II: Electron microscopy

An ultrastructural study was carried out in order to better characterize the findings observed in the first part of our study. The materials and methods are the same as those used in the preceding paper. This study reveals the occurrence of structures which display a symmetrical cross-banded pattern within the predentin and dentin of thyro-parathyroidectomized (TPTX) and parathyroidectomized (PTX) rats. A difference in the distribution of the symmetrical banded structures as dentinogenesis advances, as well as differences in the amount of the symmetrical banded structures between TPTX and PTX rats were observed. The symmetrical banded structures correspond with the so-called symmetrical SLS previously described in the incisor of normal and pathologic rats. The occurrence of these structures at a given stage of the incisor development suggests that the odontoblast is sensitive to the parathyroid hormone deficiency and/or hypocalcemia in a precise stage of its maturation.

Glycosaminoglycan and collagen fibrillar interactions in the mouse corneal stroma

When sections of mouse corneal stroma were treated with 20 mM adenosine 5'-triphosphate (ATP) in phosphate buffered saline, pH 4.0, at 37 degrees C and observed by electron microscopy, numerous periodic fibrils with about 100-nm periodicity appeared which were the aggregated form of type VI collagen (type VI collagen fibrils). They occurred in close association with D-periodic fibrillar collagens (striated collagen fibrils). However, when the tissue was digested with chondroitinase ABC or testicular hyaluronidase prior to the ATP treatment, type IV collagen fibrils were segregated from striated collagen fibrils, even though the type VI collagen fibrils themselves aggregated to form the 100 nm-periodic structures. Keratanase or Streptomyces hyaluronidase had no such effect. One possible suggestion is that the ATP-aggregated type VI collagen fibrils are connected with striated collagen fibrils through chondroitin/dermatan sulfate glycosaminoglycans.

Molecular structure and functional morphology of echinoderm collagen fibrils

The collagenous tissues of echinoderms, which have the unique capacity to rapidly and reversibly alter their mechanical properties, resemble the collagenous tissues of other phyla in consisting of collagen fibrils in a nonfibrillar matrix. Knowledge of the composition and structure of their collagen fibrils and interfibrillar matrix is thus important for an understanding of the physiology of these tissues. In this report it is shown that the collagen molecules from the fibrils of the spine ligament of a sea-urchin and the deep dermis of a sea-cucumber are the same length as those from vertebrate fibrils and that they assemble into fibrils with the same repeat period and gap/overlap ratio as do those of vertebrate fibrils. The distributions of charged residues in echinoderm and vertebrate molecules are somewhat different, giving rise to segment-long-spacing crystallites and fibrils with different banding patterns. Compared to the vertebrate pattern, the banding pattern of echinoderm fibrils is characterized by greatly increased stain intensity in the c3 band and greatly reduced stain intensity in the a3 and b2 bands. The fibrils are spindle-shaped, possessing no constant-diameter region throughout their length. The shape of the fibrils is mechanically advantageous for their reinforcing role in a discontinuous fiber-composite material.

Amino-acid sequence and cell-adhesion activity of a fibril-forming collagen from the tube worm Riftia pachyptila living at deep sea hydrothermal vents

We have determined the amino acid sequence of the alpha chain of a fibril-forming collagen from the body wall of the marine invertebrate Riftia pachyptila (vestimentifera) by Edman degradation. The pepsin-solubilized collagen chain consists of a 1011-residue triple-helical domain and short remnants of N- and C-telopeptides. The triple-helical sequence showed one imperfection of the collagen Gly-Xaa-Yaa triplet repeat structure due to a Gly-->Ala substitution. This imperfection is correlated to a prominent kink in the molecule observed by electron microscopy. No strong sequence similarity was found with the fibril-forming vertebrate collagen types I-III, V and XI except for the invariant Gly residues. However, one of the two consensus cross-linking sequences was well conserved. The Riftia collagen shared with the vertebrate collagens many post-translational modifications. About 50% of the Pro and Lys residues are found in the Yaa position and were extensively hydroxylated to 4-hydroxyproline (4Hyp) and hydroxylysine (Hyl). A few proline residues in Xaa position were partially hydroxylated to either 4Hyp or 3Hyp. Despite the low sequence similarity, Riftia collagen was a potent adhesion substrate for two human cell lines. Cell adhesion could be inhibited by antibodies against the integrin beta 1 subunit but not by RGD peptides. This biological activity is apparently conserved in fibril-forming collagens of distantly related species but does not require the two RGD sequences present in Riftia collagen.

Characterization of heterotrimeric collagen molecules in a sea-pen (Cnidaria, Octocorallia)

The collagen of a primitive invertebrate, the sea-pen Veretillum Cnidaria, Octocorallia), was studied with respect to its molecular-chain composition. The soft extracellular tissues (mesoglea) were solubilized by limited pepsin proteolysis and the collagen was isolated by selective precipitation at 0.7 M NaCl under acidic conditions. The pepsinized molecules were 260 nm in length, as demonstrated by electron microscope studies of rotary-shadowed molecules and of the segment-long-spacing crystallites obtained by dialysis against ATP. SDS/PAGE of the extract produced two main bands susceptible to bacterial collagenase, designated as the alpha 1 and alpha 2 chain, which were differentiated clearly by their CNBr cleavage products and the higher glycosylation rate of the alpha 2 chain. The latter finding corresponds with the high hydroxylysine content of the alpha 2 chain. The alpha 1/alpha 2 chain ratio observed in SDS/PAGE and the fact that only one peak was obtained by concanavalin-A affinity chromatography of a non-denatured 0.7 M NaCl extract demonstrate the alpha 1 [alpha 2]2 molecular structure of this collagen. These results contrast with data on the structure of other coelenterates (i.e. [alpha]3 for sea anemone collagen molecules and alpha 1 alpha 2 alpha 3 for jellyfish collagen molecules). They are discussed in relation to the evolution of collagen.

Molecular characterization of cuticle and interstitial collagens from worms collected at deep sea hydrothermal vents

Two different collagens were isolated and characterized from the body walls of the vestimentiferan tube worm Riftia pachyptila and the annelid Alvinella pompejana, both living around hydrothermal vents at a depth of 2600 m. The acid-soluble cuticle collagens consisted of a long triple helix (2.4 microns for Alvinella, 1.5 microns for Riftia) terminating into a globular domain. Molecular masses of 2600 and 1700 kDa, respectively, were estimated from their dimensions. The two cuticle collagens were also quite different in amino acid composition, in agreement with their different supramolecular organizations within tissues. Interstitial collagens corresponding to cross-striated fibrils underneath the epidermal cells could be solubilized by digestion with pepsin and consisted of a single alpha-chain. They were similar in molecular mass (340 kDa) and length (280 nm) but differed in composition and banding patterns of segment-long-spacing fibrils. This implicates significant sequence differences also in comparison to fibril-forming vertebrate collagens, although all form typical quarter-staggered fibrils. The thermal stability of the worm collagens was, with one exception (interstitial collagen of Riftia), in the range of mammalian and bird collagens (37 to 46 degrees C), and thus distinctly above that of shallow sea water annelids. Yet, their 4-hydroxyproline contents were not directly correlated to this stability. About 20% of Riftia collagen alpha-chain sequence was elucidated by Edman degradation and showed typical Gly-X-Y repeats but only a limited homology (45 to 58% identity) to fibril-forming vertebrate collagens. A single triplet imperfection and the variable hydroxylation of proline in the X position were additional unique features. It suggests that this collagen represents an ancestral form of fibril-forming collagens not directly corresponding to an individual fibril-forming collagen type of vertebrates.

Direct visualization of affected collagen molecules synthesized by cultured fibroblasts from an osteogenesis imperfecta patient

Human skin fibroblasts obtained from normal controls and a patient with osteogenesis imperfecta were cultured in the presence of ascorbic acid 2-phosphate, a long-acting vitamin C derivative. Crude collagen samples extracted from the cell layer were made to form lateral aggregates of collagen molecules, segment-long-spacing crystallites. Under the electron microscope, normal and abnormal crystallites of type I collagen were identified with the patient's collagen. While the carboxyl-terminal half of the abnormal crystallite was tightly packed, the amino-terminal half was loose and spreading, indicating the site of abnormality in the amino-terminal half of one of type I collagen alpha chains. The method is simple and useful to detect abnormal collagen and to predict the site of mutation.

Collagenous structures present in brain contain epitopes shared by collagen and microtubule-associated protein tau

A novel type of collagenous fibers has been isolated from human brain and characterized by electron microscopy and optical diffraction. It was found that the morphology of the fibers is similar, but not identical, to that of skin collagen. Also, the collagenous fibers show some similarities with the paracrystals that could be assembled in vitro from purified microtubule-associated protein tau. Immunological analyses indicated the presence of epitopes in these collagenous fibers which react with antibodies against collagen and tau.

Distinction between two molecular species of type V collagen from human post-burn granulation tissues

Human type V collagen was purified from post-burn granulation tissues, and was demonstrated to exist in two different molecular assemblies consisting of [alpha 1(V)]2 alpha 2(V) and alpha 1(V)alpha 2(V)alpha 3(V) heterotrimers which are designated as type V(112) and V(123) collagens, respectively, in this paper. The two molecular species were separated by salt fractionation at neutral pH under non-denaturing conditions. When crude type V collagen was dialyzed against phosphate-buffered saline at 4 degrees C, mainly collagen V(112) precipitated, leaving collagen V(123) in the solution. Type V(112) collagen, but not type V(123), precipitated at 0.15 M NaCl in 50 mM Tris-HCl buffer (pH 7.5), whereas the type V(123) molecule precipitated at 4.5 M NaCl in the same buffer. When the crude type V collagen was electrophoresed under non-denaturing conditions, two bands were observed; and it was confirmed that the fast-migrating band was composed of [alpha 1(V)]2 alpha 2(V) and the slow-migrating band was alpha 1(V)alpha 2(V)alpha 3(V). Both alpha 1 and alpha 2 chains of V(112) showed biochemical properties that were very similar, if not identical, to those of the corresponding alpha chains of V(123) judging from amino acid compositions, peptide mapping patterns obtained following treatment with cyanogen bromide and lysyl endopeptidase, and periodic acid Schiff and concanavalin A stainings. Alpha 3 chain, in contrast, was distinct from both alpha 1 and alpha 2 chains. The amino acid composition and peptide maps of alpha 3 chain were similar to some extent, but not identical, to those of the alpha 1 chain. The intensity of carbohydrate stainings of the alpha 3 chain was clearly different from that of the alpha 1 chain. The negatively stained segment-long-spacing crystallites of the two molecular species exhibited an identical banding pattern. The crystallite derived from collagen V(112) was usually in a dimeric form exhibiting the C-C terminal junction, but that of collagen V(123) was mostly in a monomeric form. Differences between the two molecular species is ascribed to the presence of the alpha 3 chain in collagen V(123).

Further evidence for the correlation between the primary structure and the stain exclusion banding pattern of the segment-long-spacing crystallites of collagen

Recently, we have noted the direct correlation between the primary structure of type I collagen and the electron microscopical banding pattern of the negatively stained segment-long-spacing (SLS) crystallites (K. Kobayashi, T. Ito, and T. Hoshino (1986), J. Electr. Microsc. 35, 272-275). In this paper, we examined the correlation in the other types of collagen. Unstained light bands (stain excluding bands) of the negatively stained SLSs of type II and type III collagens were located at the clusters of large hydrophobic amino acid residues along the respective molecules. Photographic averaging of the pattern improved the visual comparison of the correlation. We also noted a few occasions of discrepancy from the above-mentioned correlation. Preliminary computer simulation experiments revealed that, among amino acid parameters so far reported, only the hydrophobicity values of G. D. Rose and S. Roy (1980, Proc. Natl. Acad. Sci. USA 77, 4643-4647) explained the ability of amino acids for the negative staining (stain exclusion) of the collagen SLSs.

Reaggregation behavior of different types of collagen in vitro: variations in the occurrence and structure of dimeric segment long-spacing collagen

Segment long-spacing collagen (SLS) can be precipitated from solutions of collagen using ATP as the inducing agent. Dimeric SLS aggregates have been observed in addition to monomeric SLS. We have compared collagen types I, II, III, and V with respect to their ability to form dimeric SLS in vitro. These collagen types were isolated from bovine tissues and characterized by polyacrylamide slab gel electrophoresis of the respective alpha-chains. Only monomeric SLS can be detected in preparations of collagen types I and III. Dimeric SLS, on the other hand, accounts for the majority of the crystallites seen in preparations of collagen types II and V. Dimeric SLS from both collagen types II and V reveal overlap zones at the carboxy-terminal ends of the collagen molecules. However, dimeric SLS from collagen types II and V differ with respect to their overlap distances. Significant portions of the triple helical domains of collagen molecules are occupied by the overlap region of dimeric SLS from type II collagen. On the other hand, dimeric SLS from type V collagen is composed of molecules overlapping only at their short nonhelical telopeptides. It is concluded that the ability of collagen molecules to aggregate into dimeric SLS under defined experimental conditions is collagen type dependent.

Effect of polyanions on fibrillogenesis by type XI collagen

Type XI collagen (1 alpha,2 alpha,3 alpha) from bovine articular cartilage form fibrils at 4 degrees C in 0.15 M NaCl at pH 7.4, but fibrillogenesis is inhibited by the addition of 1 M glucose or by raising the NaCl concentration to 1 M. Removal of the glucose or NaCl by dialysis allows fibril formation. When proteoglycans, heparin, or chondroitin sulfate were added to type XI collagen in 1 M NaCl both fibrillogenesis and polyanion-collagen interaction were inhibited by the high NaCl concentration. When the mixture was dialysed against 0.15 M NaCl, a new aggregate type was seen, scattered among shortened and branched fibers. The new aggregates were either X-, Y-, or wheel-shaped structures with electron dense cores. They were apparently formed by collagen molecules intersecting approximately 200 nm from one end. In contrast, when the polyanion was mixed with the collagen in 1 M glucose, which inhibits fibrillogenesis but not polyanion-collagen interaction, a different type of aggregate appeared following dialysis. These aggregates were discrete 280 X 40 nm structures with an asymmetric banding pattern. They are similar to SLS aggregates, and probably are composed of collagen molecules lined up in register. The results are different from those seen with the interstitial collagens and emphasize the unique character of the interaction of polyanions, including proteoglycan, with type XI collagen.

In vitro regulation of cartilage matrix assembly by a Mr 54,000 collagen-binding protein

In cartilage, type II collagen is present as thin, short, randomly oriented fibrils. In vitro, however, type II collagen forms fibrils of large diameter, indicating that additional factors may be involved in the regulation of collagen fibril formation. We have examined extracts of a cartilage-producing tumor for the presence of collagen-binding proteins. In addition to fibronectin and link protein, a Mr 54,000 protein was found to bind to collagen fibrils as well as to native and denatured type II collagen. Immunological studies using antibody against the protein indicate that it is a cartilage matrix protein, not present in bone or in several other tissues. In vitro studies show that the Mr 54,000 protein in combination with cartilage proteoglycan decreases the rate of type II fibril formation and causes the fibrils to be of small diameter (24 +/- 8 nm). These studies indicate that complexes between collagen and proteoglycans mediated by this protein may regulate the assembly of cartilage matrix.

[Biochemical and biophysical characterization of collagen in Tenebrio molitor L. (Coleoptera, Tenebrionidae)]

The collagen from the mesenteric sheath of the tenebrionid insect Tenebrio molitor was extracted by limited pepsin digestion and purified. This collagen was characterized using CM-cellulose chromatography, sodium-dodecylsulfate disc-gel electrophoresis and aminoacid analysis. This molecule was found to be assembled from three identical alpha chains and could be represented by the formula (alpha) 3. The amino acid composition is characteristic of collagen (one-third glycine, high iminoacid content), with high content of hydroxylysine and low content of alanine. Cyanogen bromide digests of these chains indicated that they are not related to any of the known invertebrate or vertebrate chains of interstitial collagens. The molecular weight (M = 280000D) and length (290 nm) were typical, and the banding patterns of the segment-long-spacing crystallites (SLS) and of the reconstitued fibrils were very similar to type I collagen. The denaturation temperature (Td) was 30.7 degrees C and correlated with the total pyrrolidine content as observed in other collagens (von Hippel & Wong's relation). It was concluded that the collagen from this insect showed the classical biochemical and biophysical features of other invertebrate interstitial "primitive" collagens.

Isolation and partial characterization of a new human collagen with an extended triple-helical structural domain

The collagens are a family of major connective tissue proteins that are known to be the products of at least 11 distinct genes. Primary structural differences between the individual collagen types are thought to reflect functional diversity. We have isolated a previously unknown collagen gene product, termed "long-chain" (LC) collagen, from human chorioamniotic membranes by limited pepsin digestion. Comparison of the isolated alpha-chain subunit to the alpha chains of other collagen types by amino acid composition, peptide mapping with either cyanogen bromide fragmentation or staphylococcal V8 protease digestion, chromatographic elution position, and relative molecular weight indicates that this protein is a product of a previously unrecognized gene. We report structural studies indicating that this molecule contains three identical alpha-chain subunits that are each approximately molecular weight 170,000. The amino acid composition of LC alpha chains suggests that they are about 90% triple helical. Comparisons of the length of segment-long-spacing (SLS) crystallites made from LC molecules with those from types I and V collagens indicate that the LC molecule is substantially longer than these collagens and somewhat longer than the reported length of type IV collagen. This finding suggests that LC collagen represents an additional class of collagen molecules. We suggest that these molecules be referred to as type VII collagen.