We have characterized a mutation in the type II collagen gene (COL2AJ) that produces a form of spondyloepiphyseal dysplasia. The mutation is an internal tandem duplication of 45 base pairs within exon 48 and results in the addition of 15 amino acids to the triple-helical domain of the al chains of type II collagen derived from the abnormal allele.Although the repeating (Gly-Xaa-Yaa)1. motif that characterizes the triple-helical domain is preserved, type H collagen derived from cartilage of the affected individual contains a population with excessive posttranslational modification, consistent with a disruption in triple-helix structure. The mutation is not carried by either parent, indicating that the phenotype in the affected individual is due to a new dominant mutation. DNA sequence homology in the area of the duplication suggests that the mutation may have arisen by unequal crossover between related sequences, a proposed mechanism in the evolution and diversification of the collagen gene family.The spondyloepiphyseal dysplasias (SEDs) are a heterogeneous subgroup of the skeletal dysplasias whose cardinal features include abnormal epiphyses, flattened vertebral bodies, and ocular involvement that ranges from myopia to vitreo-retinal degeneration (1). Since type II collagen is found in a restricted set of tissues that includes articular cartilage, the nucleus pulposus of the spine, and the vitreous of the eye (2), the concordance between the clinical findings and the distribution of the protein suggests that a primary defect of type II collagen may be responsible for some of these disorders. Structurally abnormal type II collagen has been isolated from cartilage ofindividuals with SED (3, 4), spondyloepimetaphyseal dysplasia (3,4), and achondrogenesishypochondrogenesis (5). Combined with the demonstration of linkage of markers in the COL2AJ gene with a form of familial osteoarthritis (6) and with Stickler syndrome (7,8), these studies have suggested that mutations in the type II collagen gene may underlie a spectrum of disorders that span a broad range of clinical severity.Type II collagen is a fibrillar collagen that in its mature form is a homotrimer ofal(II) chains (9). Biochemical studies have shown that cartilage from individuals with either SED (3, 4) or achondrogenesis-hypochondrogenesis (5) contains type II collagen with both slowly migrating and normally migrating al(II) chains. Amino acid analyses of the abnormal type II collagen from the affected individuals have shown that there is increased lysyl hydroxylation (3-5), suggesting that the more slowly migrating population is derived from molecules containing a chain with a defect that affects triple-helix structure and/or assembly. These results are conceptually homologous to the consequences of defects in type I collagen that produce osteogenesis imperfecta, in which mutations that alter triple-helix structure result in excessive posttranslational modification of all chains in molecules that incorporate at least one abnormal chain (10, 11). Th...

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...

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In order to elucidate the biochemical mechanism of laser welding of tissues, we have compared protein profiles from argon laser-treated specimens with controls. Extracellular matrix components from untreated and laser-welded skin and blood vessels were extracted with guanidine hydrochloride and separated by SDS polyacrylamide gel electrophoresis. When compared with matched, untreated tissues, protein electrophoretic profiles from laser-treated samples showed several changes. In both tissue types, argon laser treatment decreased the concentration of a 235 kd protein that migrates between the alpha and beta chains of type I collagen. Laser-treated blood vessels showed significantly more low molecular weight protein at the dye front than in control tissue, whereas significantly more high molecular weight protein appeared in laser-treated skin samples when compared with untreated tissue. These results suggest that the argon laser may either degrade or crosslink proteins in vivo. Laser-induced protein crosslinks may be the biochemical basis of argon laser welding.