Distinct Maturations of N-propeptide Domains in Fibrillar Procollagen Molecules Involved in the Formation of Heterotypic Fibrils in Adult Sea Urchin Collagenous Tissues

Abstract

We have characterized the primary structure of a new sea urchin fibrillar collagen, the 5␣ chain, including nine repeats of the sea urchin fibrillar module in its N-propeptide. By Western blot and immunofluorescence analyses, we have shown that 5␣ is co-localized in adult collagenous ligaments with the 2␣ fibrillar collagen chain and fibrosurfin, two other extracellular matrix proteins possessing sea urchin fibrillar modules. At the ultrastructural level, the 5␣ N-propeptide is detected at the surface of fibrils, suggesting the retention of this domain in mature collagen molecules. Biochemical characterization of pepsinized collagen molecules extracted from the test tissue (the endoskeleton) together with a matrix-assisted laser desorption ionization timeof-flight analysis allowed us to determine that 5␣ is a quantitatively minor fibrillar collagen chain in comparison with the 1␣ and 2␣ chains. Moreover, 5␣ forms heterotrimeric molecules with two 1␣ chains. Hence, as in vertebrates, sea urchin collagen fibrils are made up of quantitatively major and minor fibrillar molecules undergoing distinct maturation of their N-propeptide regions and participating in the formation of heterotypic fibrils.Among the components of extracellular matrix, collagens are the most abundant of the glycoproteins. In vertebrates, 27 collagen types have been identified (1-4). All of them consist of three identical or different ␣ chains that contain at least one collagenous or triple helical segment, consisting of repeating Gly-Xaa-Xaa triplets. The collagen domains of the three ␣ chains coil around each other into a triple helical structure. The fibrillar collagens, including types I-III, V, and XI, are the best known, and their precursor ␣ chains consist of a main triple helix made up of ϳ338 Gly-Xaa-Xaa triplets flanked by two non-collagenous regions containing the N-and the C-propeptides. During maturation of procollagens into collagen molecules, the two propeptide domains are generally removed by the action of specific proteinases (1). The resulting collagen molecules participate in the formation of supramolecular structures called fibrils. The invertebrate fibrillar ␣ chains so far described present the same overall structure as that of their vertebrate counterparts (5).In different sea urchin species, studies have indicated the presence of two fibrillar ␣ chains (1␣ and 2␣) involved in the formation of heterotrimeric molecules [(1␣) 2 -2␣] (6 -8). Moreover, traces of a homotrimeric 1␣ chain have been described in the sea urchin Paracentrotus lividus (9). The complete primary structure of these two fibrillar collagen chains has been characterized in the sea urchin Strongylocentrotus purpuratus (10,

Invertebrate Data Predict an Early Emergence of Vertebrate Fibrillar Collagen Clades and an Anti-incest Model

“…bcm.tmc.edu. From this analysis, we were able to discover two regions of the S. purpuratus genome encoding the C terminus of a classical C-propeptide distinct from the three previously characterized sea urchin fibrillar collagen chains (17)(18)(19). The two sequence files corresponded to Contig18666 and Contig84214 and encoded part of the fibrillar collagens termed 6␣ and 7␣, respectively, in this study.…”

“…They can be divided quantitatively into major (1␣ and 2␣) and minor (5␣) collagen chains (17). Blast searching of the S. purpuratus genome resources using a sequence encoding the 1␣ C-propeptide allowed us to identify two genomic sequences encoding the C-terminal part of the C-propeptides unrelated to those of the three known sea urchin fibrillar collagens.…”

“…Three sea urchin fibrillar collagen chains (1␣, 2␣, and 5␣) have previously been characterized (17)(18)(19). They can be divided quantitatively into major (1␣ and 2␣) and minor (5␣) collagen chains (17).…”

“…One explanation for this conundrum is that almost all the invertebrate fibrillar chains described to date are quantitatively major ones and that, like their vertebrate counterparts, they possess a vWc module in their N-propeptide. However, we have recently shown that sea urchin also possesses a quantitatively minor fibrillar collagen chain (17).…”

Interfibrillar stiffening of echinoderm mutable collagenous tissue demonstrated at the nanoscale

“…Biochemical evidence to support this hypothesis includes the structural similarity of some of these proteins to the tissue inhibitors of matrix metalloproteinases (TIMPs) found in vertebrates (39). Consistent with this notion, it has also been suggested that cysteine-rich sea urchin fibrillar domains (SURFs), found so far in the sea urchin collagen 2α and 5α N-propeptides, as well as fibrosurfin (an interfibrillar protein) (36,40), play a role in enabling mutability. The 2α N-propeptides and fibrosurfin colocalize on collagen fibril surfaces in adult sea urchins.…”