ATYPICAL GLY-X-Y SEQUENCES SURROUND INTERRUPTIONS IN THE REPEATING TRIPEPTIDE PATTERN OF BASEMENT-MEMBRANE COLLAGEN

The triple-helical domains of type IV collagen chains have more than 2 0 sites at which the repeating (Gly-X-Y)(n) pattern is interrupted. An alysis of alpha 1 (IV) and alpha 2(IV) chains indicates the residues i n the three Gly-X-Y triplets preceding or following interruptions diff er statistically from the rest of the chain. Unusually high frequencie s of charged residues are seen at a number of X and Y sites, with the charge density being particularly high C-terminal to the interruption site. Analyses were carried out on individual categories of interrupti ons, classified as insertions or deletions in the Y position. All of t he residues in the X and Y positions of the triplets flanking insertio n sites are atypical, with a high concentration of charged residues. T riplets flanking sites where there has been a deletion in the Y positi on show unusually high frequencies of charged residues at some sites, hydrophobic residues at other sites, and an invariant imino acid N-ter minal to the interruption. The presence of atypical sequences surround ing interruptions could le important at a molecular level, related to triple-helix stability, or at a supramolecular level, related to the a ssociation of molecules to form networks in basement membranes. (C) 19 95 John Wiley & Sons, Inc.