The structure of fibril-forming collagens

Proteoglycan-fibrillar collagen interactions

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Collagen components of bovine fetal and guinea pig cochlear bone and human stapes

Collagenous components were isolated chemically from fetal bovine or guinea pig cochlear bone and human stapes after stapedectomy, and the purified protein was characterized by immunoblot assay and amino acid analysis. The results of this study suggest that these are mixtures of type I and type II collagens. The presence of type II collagen in the human stapes also was demonstrated by immunohistologic methods using monoclonal antibody. The presence of type II collagen in these tissues is significant, since it has been postulated as an autoantigen in autoimmune inner ear disease.

Autoantibodies to type II collagen: occurrence in rheumatoid arthritis, other arthritides, autoimmune connective tissue diseases, and chronic inflammatory syndromes

Serum IgG antibodies to native and denatured human type II collagen (Col II) were measured using an enzyme linked immunosorbent assay (ELISA). One hundred and thirty one patients with various forms of arthritis such as rheumatoid arthritis (RA), ankylosing spondylitis (AS), psoriatic arthritis (PSA). Reiter's Syndrome (RS), osteoarthritis (OA), and gout, 60 with autoimmune connective tissue disease, and 37 with the chronic inflammatory conditions--graft versus host disease and leprosy--were studied. With the exception of RS, PSA, OA, and gout, significant levels of Col II antibodies were detected in each disease group. Blocking studies with types I and II collagen on selected serum samples confirmed the specificity to native Col II, though some cross reactivity was apparent with denatured collagen. The patients with RA who were Col II antibody positive tended to fall into stage III of disease progression. There was, however, no correlation with rheumatoid factor, erythrocyte sedimentation rate, or disease duration and this, together with the finding that Col II antibodies are present in a wide array of diseases, makes their role in the pathogenesis of RA questionable. They may arise as a secondary disease perpetuating mechanism in some patients, or in turn may be an epiphenomenon secondary to generalised disturbed immunoregulation or B cell hyperreactivity, or both, that characterises these clinical conditions.

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.

Complete primary structure of the alpha 1-chain of human basement membrane (type IV) collagen

We have determined the primary structure of the alpha 1(IV)-chain of human type IV collagen by nucleotide sequencing of overlapping cDNA clones that were isolated from a human placental cDNA library. The present data provide the sequence of 295 amino acids not previously determined. Altogether, the alpha 1(IV)-chain contains 1642 amino acids and has a molecular mass of 157625 Da. There are 1413 residues in the collagenous domain and 229 amino acids in the carboxy-terminal globular domain. The human alpha 1(IV)-chain contains a total of 21 interruptions in the collagenous Gly-X-Y repeat sequence. These interruptions vary in length between two and eleven residues. The alpha 1(IV)-chain contains four cysteine residues in the triple-helical domain, four cysteines in the 15-residue long noncollagenous sequence at the amino-terminus and 12 cysteines in the carboxy-terminal NC-domain.

Expression of a metalloproteinase that degrades native type V collagen and denatured collagens by cultured human alveolar macrophages

Human pulmonary alveolar macrophages obtained by bronchoalveolar lavage from both normal controls and smokers secreted in vitro a neutral proteinase that degraded denatured collagens. Optimal expression of the proteinase was detected after 3-5 d of culture. The proteinase could not be detected in the media of cultures that had been treated with 0.5 micrograms/ml of cycloheximide. The gelatinase had an Mr of 90,000 and was immunologically cross-reactive with human neutrophil gelatinase. When newly synthesized 35S-methionine-labeled proteins were analyzed, the proteinase appeared to be a major secretion product of alveolar macrophages. Chromatography on gelatin-Sepharose gave a single peak of activity that was predominantly composed of the 90,000-mol-wt proteinase. The proteolytic activity in the gelatin-Sepharose-purified material was inhibited by EDTA and 1,10-phenanthroline, but not by N-ethylmaleimide or phenylmethanesulfonyl fluoride, indicating that the proteinase was a metalloproteinase. The partially purified material was also capable of degrading native type V collagen and this degradation was inhibited in the presence of an antibody to neutrophil gelatinase. The data suggest that human alveolar macrophages in culture elaborate a metalloproteinase that degrades both native type V collagen and denatured collagens.

Type VI collagen of the intervertebral disc. Biochemical and electron-microscopic characterization of the native protein

The collagen framework of the intervertebral disc contains two major fibril-forming collagens, types I and II. Smaller amounts of other types of collagen are also present. On examination of the nature and distribution of these minor collagens within bovine disc tissue, type VI collagen was found to be unusually abundant. It accounted for about 20% of the total collagen in calf nucleus pulposus, and about 5% in the annulus fibrosus. It was discovered by serially digesting disc tissue with chondroitin ABC lyase and Streptomyces hyaluronidase that native covalent polymers of type VI collagen could be extracted. Electron micrographs of this material prepared by rotary shadowing revealed the characteristic dimensions of tetramers and double tetramers of type VI molecules, with their central rods and terminal globular domains. Molecular-sieve column chromatography on agarose under non-reducing non-denaturing conditions gave a series of protein peaks with molecular sizes equivalent to the tetramer, double tetramer and higher multimers. On SDS/polyacrylamide-gel electrophoresis after disulphide cleavage, these fractions of type VI collagen all showed a main band at Mr 140,000 and four lesser bands between Mr 180,000 and 240,000. On electrophoresis without disulphide cleavage in agarose/2.4% polyacrylamide only dimeric (six chains) and tetrameric (12 chains) forms of type VI molecules were present. The ability to extract all the type VI collagen of the tissue in 4 M-guanidinium chloride, and absence of aldehyde-mediated cross-linking residues on direct analysis, showed that, in contrast with most matrix collagens, type VI collagen does not function as a covalently cross-linked structural polymer.

Extensive structural differences between genes for the alpha 1 and alpha 2 chains of type IV collagen despite conservation of coding sequences

Analysis of the structure of the 3'-end of the human alpha 2(IV) gene demonstrated that the alpha 1(IV) and alpha 2(IV) genes have diverged extensively in spite of the apparent homology of the respective gene products. The NC-1 domain and the 3'-untranslated region are encoded by three exons in the alpha 2(IV) gene but five exons in the alpha 1(IV) gene. The two introns present in the NC-1 domain coding part of the alpha 2(IV) gene had the same location as two of the introns of the alpha 1(IV) gene. The junction exon in the alpha 2(IV) gene contains 53 bp coding for Gly-X-Y sequences whereas there are 71 bp in the alpha 1(IV) gene. Three other Gly-X-Y coding exons studied from the human alpha 2(IV) gene have sizes that differ from corresponding exons in the alpha 1(IV) gene and only one intron location matches here between the two genes. None of the exons studied has 54 bp or multiples thereof.

Type III collagen can be present on banded collagen fibrils regardless of fibril diameter

Monoclonal antibodies that recognize an epitope within the triple helix of type III collagen have been used to examine the distribution of that collagen type in human skin, cornea, amnion, aorta, and tendon. Ultrastructural examination of those tissues indicates antibody binding to collagen fibrils in skin, amnion, aorta, and tendon regardless of the diameter of the fibril. The antibody distribution is unchanged with donor age, site of biopsy, or region of tissue examined. In contrast, antibody applied to adult human cornea localizes to isolated fibrils, which appear randomly throughout the matrix. These studies indicate that type III collagen remains associated with collagen fibrils after removal of the amino and carboxyl propeptides, and suggests that fibrils of skin, tendon, and amnion (and presumably many other tissues that contain both types I and III collagens) are copolymers of at least types I and III collagens.

Type XII collagen: distinct extracellular matrix component discovered by cDNA cloning

We have screened a cDNA library constructed from tendon fibroblast mRNA for the presence of collagenous coding sequences. Nucleotide sequence analysis of one isolated clone, pMG377, reveals that the clone encodes a polypeptide that is homologous to, yet distinctly different from, type IX short-chain collagen polypeptides. The structure of the conceptual translation product of the cDNA is also different from that of all other collagen types. Therefore, we have given the type IX-like collagen chain encoded by pMG377 the designation alpha 1(XII). Ribonuclease protection assays with single-stranded cRNA probes demonstrate that alpha 1(XII) mRNA is present in several tissues such as calvaria, tendon, and sternal cartilage of 17-day-old chicken embryo and in cornea from 6-day-old embryos. Using pMG377 as the hybridization probe, we isolated a fragment of the corresponding gene from a chicken genomic library. Partial nucleotide sequence analysis of the genomic clone DG12 shows that the exon/intron structure of the alpha 1(XII) collagen gene appears to be homologous to that of the alpha 1(IX) and alpha 2(IX) collagen genes. Our data demonstrate that types IX and XII collagen are two homologous members of a family of unique collagenous proteins that show tissue-specific patterns of expression. Based on their structure and the properties of their genes, we conclude that this family of collagens is distinctly different from that of fibrillar collagens.

Enchondral cartilage rests collagen-induced autoimmunity: a possible pathogenetic mechanism of otosclerosis

Collagen autoimmunity has been suggested as one etiologic mechanism to otosclerosis. Although substantial studies relating this disease to collagen autoimmunity have been reported, a basic understanding of the pathogenic mechanism involved is lacking. Some otosclerosis patients have a high level of antibody to type II collagen. In addition, complement and antibody were deposited in the stapes from otosclerosis patients. Furthermore, the otic capsule and stapes have been found to contain type II collagen by immunohistologic studies and biochemical analysis. Otospongiosis-like lesions have also been produced in rats by immunizing them with type II collagen. This finding led us to postulate a hypothesis of an autoimmunity to type II collagen as an etiopathogenesis of this illness. Our initial hypothesis has been updated to incorporate new findings in the field of cell biology. The role of interleukin 1, osteoclasts, osteoblasts, bone resorption, and other factors such as minor collagens, calcitonin, vitamin D, parathyroid hormone, collagenase, and prostaglandins are incorporated in this updated hypothesis.

Identification of the complement decay-accelerating factor (DAF) on epithelium and glandular cells and in body fluids

Decay-accelerating factor (DAF) is a 70 kD membrane regulatory protein that prevents the activation of autologous complement on cell surfaces. Using immunohistochemical methods and a radioimmunometric assay based on mAbs to DAF, we found large amounts of membrane-associated DAF antigen on the epithelial surface of cornea, conjunctiva, oral and gastrointestinal mucosa, exocrine glands, renal tubules, ureter and bladder, cervical and uterine mucosa, and pleural, pericardial and synovial serosa. Additionally, we detected soluble DAF antigen in plasma, tears, saliva, and urine, as well as in synovial and cerebrospinal fluids. While plasma, tear, and saliva DAF are larger than erythrocyte (Ehu) membrane DAF by Western blot analysis, urine DAF is slightly smaller (67,000) in Mr. Unlike purified Ehu DAF, however, urine DAF is unable to incorporate into the membrane of red cells. Although its inhibitory activity on the complement enzyme C3-convertase is lower than that of Ehu DAF, it is comparable to that of serum C4 binding protein (C4bp). Biosynthetic studies using cultured foreskin epithelium and Hela cells disclosed DAF levels (approximately 2 X 10(5) molecules/cell) exceeding those on blood cells. In addition, these studies revealed the synthesis of two DAF species, one with apparent Mr corresponding to that of epithelial cell membrane DAF and the other to urine DAF, suggesting that the urine DAF variant arises from adjacent epithelium. The function of DAF in body fluids is unknown, but the observation that urine DAF has C4bp-(or factor H-)like activity shows that it could inhibit the fluid phase activation of the cascade.

The pro alpha 2(V) collagen gene is evolutionarily related to the major fibrillar-forming collagens

A number of overlapping cDNA clones, covering 5.2 kb of sequences which code for the human pro alpha 2(V) collagen chain, have been isolated. Analysis of the structural data have indicated a close evolutionary kinship between the pro alpha 2(V) chain and the major fibrillar collagen types. Isolation and analysis of an 8 kb genomic fragment has further supported this notion by revealing a homologous arrangement of nine triple-helical domain exons. These studies have therefore provided conclusive evidence which categorizes the Type V collagen as a member of the Group 1 molecules, or fibrillar-forming collagens.