Type V collagen: molecular structure and fibrillar organization of the chicken alpha 1(V) NH2-terminal domain, a putative regulator of corneal fibrillogenesis.

Abstract

Abstract. Previous work from our laboratories has demonstrated that: (a) the striated collagen fibrils of the corneal stroma are heterotypic structures composed of type V collagen molecules coassembled along with those of type I collagen, (b) the high content of type V collagen within the corneal collagen fibrils is one factor responsible for the small, uniform fibrillar diameter (25 nm) characteristic of this tissue, (c) the completely processed form of type V collagen found within tissues retains a large noneollagenous region, termed the NH2-terminal domain, at the amino end of its txl chain, and (d) the NH2-terminal domain may contain at least some of the information for the observed regulation of fibril diameters. In the present investigation we have employed polyclonal antibodies against the retained NH2-terminal domain of the ot 1 (V) chain for immunohistochemical studies of embryonic avian corneas and for immunoscreening a chicken cDNA library. When combined with cDNA sequencing and molecular rotary shadowing, these approaches provide information on the molecular structure of the retained NH2-terminal domain as well as how this domain might function in the regulation of fibrillar structure.In immunofluorescence and immunoelectron microscopy analyses, the antibodies against the NH2-terminal domain react with type V molecules present within mature heterotypic fibrils of the corneal stroma. Thus, epitopes within at least a portion of this domain are exposed on the fibril surface. This is in marked contrast to mAbs which we have previously characterized as being directed against epitopes located in the major triple helical domain of the type V molecule. The helical epitopes recognized by these antibodies are antigenically masked on type V molecules that have been assembled into fibrils. Sequencing of the isolated eDNA clones has provided the conceptual amino acid sequence of the entire amino end of the cd(V) procollagen chain. The sequence shows the location of what appear to be potential propeptidase cleavage sites. One of these, if preferentially used during processing of the type V procollagen molecule, can provide an explanation for the retention of the NH2-terminal domain in the completely processed molecule. The sequencing data also suggest that the NH2-terminal domain consists of several regions, providing a structure which fits well with that of the completely processed type V molecule as visualized by rotary shadowing.T HE major component of the mature corneal stroma is a striated collagen fibril characterized by its small, uniform diameter (25 /tm). Because these fibrillar properties are thought to be required for corneal transparency, elucidating the molecular mechanism(s) by which they are controlled is paramount to our understanding of the development and growth of a functional cornea, as well as of fibrillogenesis in general.

Comparative ultrastructure of collagen fibrils in uterine leiomyomas and normal myometrium

“…We observed collagen fibrils with an ordered and regular barbed appearance in the myometrium (Fig. 2B), which resembles that observed in chick corneas (26). The appearance of these fibrils in electron micrographs along with amino acid sequence data suggests that type V collagen molecules may occur within a heterotypic type I + V collagen fibril.…”

“…In addition to the effect of procollagen processing and glycosylation of collagen molecules and collagen-proteoglycan interactions on the formation of fibrils, it has been shown that the interaction of two or more different types of fibrillar collagen chains may interact and result in the formation of heterotypic fibrils (23)(24)(25)(26). We observed collagen fibrils with an ordered and regular barbed appearance in the myometrium (Fig.…”

The bone morphogenetic protein 1/Tolloid-like metalloproteinases

“…It is the proteolytically trimmed amino-terminal globular sequences of the minor fibrillar collagen chains that are thought to regulate the shapes and diameters of heterotypic fibrils (Linsenmayer et al, 1993). Thus, proteolytic trimming of the amino-terminal globular sequences of minor fibrillar procollagen chains appears to be another way in which the BMP1/ TLD-like proteinases regulate collagen fibrillogenesis.…”

Analysis of transcriptional isoforms of collagen types IX, II, and I in the developing avian cornea by competitive polymerase chain reaction

“…In the secondary corneal stroma, the small diameters of the collagen fibrils are thought to result from the incorporation of a relatively large proportion of type V collagen into heterotypic type I + V fibrils (Doane et al, 1992;Birk et al, 1990); control of fibril diameter is 43 thought to be exerted by the presence of a large aminoterminal globular domain of type V (Linsenmayer et al, 1993) that serves to inhibit lateral growth of the fibril. It is reasonable to assume that fibril diameter in the primary stroma is controlled in a similar fashion, but by a different collagen type (see below): these fibrils contain, along with type I collagen, type I1 collagen instead of type V.…”