The Role of Disulfide Bonds and α-Helical Coiled-coils in the Biosynthesis of Type XIII Collagen and Other Collagenous Transmembrane Proteins

Anne Latvanlehto,Anne Tuomisto,Anne Snellman,Taina Pihlajaniemi,Anu Koski

doi:10.1074/jbc.m609605200

Abstract

Type XIII collagen is a type II transmembrane protein with three collagenous (COL1-3) and four noncollagenous domains (NC1-4). The human alpha1(XIII) chain contains altogether eight cysteine residues. We introduced point mutations to six of the most N-terminal cysteine residues, and we show here that the two cysteines 117 and 119 at the end of the N-terminal noncollagenous domain (NC1) are responsible for linking the three alpha1(XIII) chains together by means of interchain disulfide bonds. In addition, the intracellular and transmembrane domains have an impact on trimer formation, whereas the cysteines in the transmembrane domain and the COL1, the NC2, and the C-terminal NC4 domains do not affect trimer formation. We also suggest that the first three noncollagenous domains (NC1-3) harbor repeating heptad sequences typical of alpha-helical coiled-coils, whereas the conserved NC4 lacks a coiled-coil probability. Prevention of the coiled-coil conformation in the NC3 domain is shown here to result in labile type XIII collagen molecules. Furthermore, a new subgroup of collagenous transmembrane proteins, the Rattus norvegicus, Drosophila melanogaster, and Caenorhabditis elegans colmedins, is enlarged to contain also Homo sapiens collomin, and Pan troglodytes, Mus musculus, Tetraodon nigroviridis, and Dano rerio proteins. We suggest that there is a structurally varied group of collagenous transmembrane proteins whose biosynthesis is characterized by a coiled-coil motif following the transmembrane domain, and that these trimerization domains appear to be associated with each of the collagenous domains. In the case of type XIII collagen, the trimeric molecule has disulfide bonds at the junction of the NC1 and COL1 domains, and the type XIII collagen-like molecules (collagen types XXIII and XXV) and the colmedins are similar in that they all have a pair of cysteines in the same location. Moreover, furin cleavage at the NC1 domain can be expected in most of the proteins.

Highlights

Ria; it should be a type II transmembrane protein with at least one collagenous domain
We have studied the biosynthetic features of type XIII collagen by expressing it in insect cells using the baculovirus expression system, and we have demonstrated a disulfide-bonded homotrimeric molecule with three triple helical collagenous domains [3]
We have shown in previous studies that some of the cysteines in the NC1 domain of human type XIII collagen, and possibly those at the junction of the

Summary

Introduction

Ria; it should be a type II transmembrane protein with at least one collagenous domain. The significance of the NC3 coiled-coil domain for the biosynthesis of stable type XIII collagen molecules was addressed; and third, the COL2del mutant molecules were produced in insect cells, allowing assessment of the effects of a shortened COL2 and lack of the most C-terminal cysteine pair on the formation of disulfide-bonded triple-helical molecules.

Results

Conclusion