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

Abstract

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 a-chain subunit to the a 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 a-chain subunits that are each approximately molecular weight 170,000. The amino acid composition of LC a 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.Human connective tissues are known to contain multiple collagen types (1, 2). Documented structural differences between the collagen types suggest that they serve unique functions and are, in part, responsible for the variations in biochemical and physiological properties observed between different connective tissues (2). For example, the interstitial collagens (types I, II, and III) all have the same helical length (3), are ultimately post-translationally processed to a similar degree (4), are susceptible to the same degradative enzyme systems (5), and by aligning in D-staggered array, form banded fibers that are stabilized by lysine and hydroxylysine-derived crosslinks (6). In contrast, type IV collagen in basement membranes is not proteolytically processed extracellularly (7)(8)(9), has regions of increased flexibility and susceptibility to various proteases (10-12), has a triple-helical domain 1.3 times the length of type I collagen (13)(14)(15), and has been shown to form a fiber system dependent upon the presence of molecular domains that are analogous to the interstitial collagen propeptides (16). This fiber system is believed to be unique to basement membrane collagen and to underlie the distinct function of that specialized connective tissue structure.Type V procollagen has been shown to undergo only a limited degree of proteolytic processing (17-19). The structure of the matrix form of these molecules is unknown, but one would predict that its fiber form might be different from that of the interstitial collagens or of basement membrane collagen.Recently, several additional collagenous pro...

Number and organization of collagen genes in Caenorhabditis elegans.

“…Our best estimates, based on genomic Southern blot hybridization experiments and recombinant phage library screenings, are that C. elegans has at least 40 and as many as 150 distinct collagen genes. The number of collagen genes in C. elegans is much larger than that reported for any other organism, e.g., humans, in which 10 to 20 genes at most have been identified (3,4). In addition to their larger number, C. elegans collagen genes differ from other known collagen genes by their small size.…”

“…Collagens have been extensively studied in vertebrates, in which at least nine collagen types, with specific tissue distributions and structural properties, have been described (3,4,16). Protein sequencing coupled with protease and chemical cleavage studies has shown that the different collagen types have unique primary sequences and are coded for by 10 to 20 genes (3, 4).…”

“…Synchronous populations of nematodes were started from dauer larvae (11) or from firststage larvae synchronized by hatching eggs in M9 buffer (5) in the absence of a food source (15,3). Molting periods were monitored by observing pharyngeal pumping movements under a dissecting microscope (6 Fig.…”

Synthesis and characterization of cDNA encoding a cartilage-specific short collagen.

“…Thus, while type I collagen is the major collagen of bone, skin, tendons, and ligaments, type II collagen is found primarily in hyaline cartilage, and type IV collagen is the collagen of basement membranes. In addition, types III, V, VI, and VII collagens (1)(2)(3)(4)(5)(6)(7)(8)(9) show characteristic tissue distributions, which probably reflect their specific functions in different tissues.…”

Stage-specific patterns of collagen gene expression during development of Caenorhabditis elegans.

“…All collagens share a characteristic amino acid sequence which can be represented as (Gly-X-Y), where X and Y can be any amino acids but are often proline or hydroxyproline. Collagens have been extensively studied in vertebrates, for which at least nine collagen types with different protein sequences and tissue distributions have been described (3,5). For the past few years, we have been studying the collagen gene family of the soil nematode Caenorhabditis elegans.…”