Glycosylated threonine but not 4-hydroxyproline dominates the triple helix stabilizing positions in the sequence of a hydrothermal vent worm cuticle collagen

Structure, function and tissue forms of the C-terminal globular domain of collagen XVIII containing the angiogenesis inhibitor endostatin

The C-terminal domain NC1 of mouse collagen XVIII (38 kDa) and the shorter mouse and human endostatins (22 kDa) were prepared in recombinant form from transfected mammalian cells. The NC1 domain aggregated non-covalently into a globular trimer which was partially cleaved by endogenous proteolysis into several monomers (25-32 kDa) related to endostatin. Endostatins were obtained in a highly soluble, monomeric form and showed a single N-terminal sequence which, together with other data, indicated a compact folding. Endostatins and NC1 showed a comparable binding activity for the microfibrillar fibulin-1 and fibulin-2, and for heparin. Domain NC1, however, was a distinctly stronger ligand than endostatin for sulfatides and the basement membrane proteins laminin-1 and perlecan. Immunological assays demonstrated endostatin epitopes on several tissue components (22-38 kDa) and in serum (120-300 ng/ml), the latter representing the smaller variants. The data indicated that the NC1 domain consists of an N-terminal association region (approximately 50 residues), a central protease-sensitive hinge region (approximately 70 residues) and a C-terminal stable endostatin domain (approximately 180 residues). They also demonstrated that proteolytic release of endostatin can occur through several pathways, which may lead to a switch from a matrix-associated to a more soluble endocrine form.

Structural analysis and proteolytic processing of recombinant G domain of mouse laminin alpha2 chain

Four individual LG modules from the C-terminus of the laminin alpha2 chain (LG1, LG2, LG4 and LG5) and combinations of these modules were prepared as recombinant products from transfected mammalian cells. This demonstrated that LG modules represent autonomously folding protein domains. Successful production depended on proper alignment of module borders and required a sequence correction at the C-terminus which added an extra cysteine. The LG modules were glycosylated and shown by electron microscopy to have a globular shape, indicating proper folding. Evidence is provided for the splicing of a 12 bp exon in LG2, although this did not impair folding. Proteolytic cleavage at the C-terminus of a basic sequence was observed close to the N-terminus of LG3. A similar processing also occurs in tissue-derived laminin-2 and -4 which contain the alpha2 chain.

Dimer model for the microfibrillar protein fibulin-2 and identification of the connecting disulfide bridge

Fibulin-2 is a novel extracellular matrix protein frequently found in close association with microfibrils containing either fibronectin or fibrillin. The entire protein and its predicted domains were obtained as recombinant products and examined by ultracentrifugation and electron microscopy. This demonstrated a disulfide-linked homodimer of 175 kDa subunits. Partial reduction to monomers identified specifically an odd Cys574 residue responsible for dimer formation in one of three anaphylatoxin-like modules that constitute the central globular domain I (13 kDa) of fibulin-2. Furthermore, a Cys574-Ser mutation abolished disulfide connection but not non-covalent dimerization of fibulin-2. The C-terminal region (85 kDa) was shown to represent a 35-nm-long rod consisting of 11 calcium-binding EGF-like modules (domain II) and a small terminal globe (domain III). The unique N-terminal domain N (55 kDa) was also rod-shaped (approximately 38 nm) and rich in galactosamine indicating extensive O-glycosylation. A dimer model is proposed indicating mainly a rod-like shape of 80 nm length based on an anti-parallel association of two subunits through their domains I. This model also implies alignment of domains II and N between different subunits. This was demonstrated by surface plasmon resonance assay which showed a distinct interaction between domains N and II with a Kd of approximately 0.7 microM.

Cloning of an annelid fibrillar-collagen gene and phylogenetic analysis of vertebrate and invertebrate collagens

Arenicola marina possesses cuticular and interstitial collagens, which are mostly synthesised by its epidermis. A cDNA library was constructed from the body wall. This annelid cDNA library was screened with a sea-urchin-collagen cDNA probe, and several overlapping clones were isolated. Nucleotide sequencing of these clones revealed an open reading frame of 2052 nucleotides. The translation product exhibits a triple helical domain of 138 Gly-Xaa-Yaa repeats followed by a 269-residue-long C-terminal non-collagenous domain (C-propeptide). The triple helical domain exhibits an imperfection that has been previously described in a peptide produced by cyanogen bromide digestion (CNBr peptide) of A. marina interstitial collagen. This imperfection occurs at the same place in the interstitial collagen of the vestimentiferan Riftia pachyptila. This identifies the clone as coding for the C-terminal part of a fibrillar collagen chain. It was called FAm1alpha, for fibrillar collagen 1alpha chain of A. marina. The non-collagenous domain possesses a structure similar to carboxy-terminal propeptides of fibrillar pro-alpha chains. Only six conserved cysteine residues are observed in A. marina compared with seven or eight in all other known C-propeptides. This provides information on the importance of disulfide bonds in C-propeptide interactions and in the collagen-assembly process. Phylogenetic studies indicate that the fibrillar collagen 1alpha chain of A. marina is homologous to the R. pachyptila interstitial collagen and that the FAm1alpha gene evolved independently from the other alpha-chain genes. Complementary analyses indicate that the vertebrate fibrillar collagen family is composed of two monophyletic subgroups with a specific position of the collagen type-V chains.