NMR-STUDIES OF PEPTIDES DERIVED FROM THE PUTATIVE BINDING REGIONS OF CARTILAGE PROTEINS - NO EVIDENCE FOR BINDING TO HYALURONAN

Previous work has implicated sequences within the tandem repeats of ca rtilage link protein in the interaction of link protein with hyalurona n. This conclusion was based on competitive inhibition experiments usi ng synthetic peptides (Goetinck, P. F., Stirpe, N. S., Tsonis, P. A., and Carlone, D. (1987) J. Cell Biol. 105, 2403-2407). Further investig ation of this system using high resolution nuclear magnetic resonance, circular dichroism, and competitive inhibition with other peptides in dicates that the previously observed inhibition of link protein-hyalur onan binding was not caused by peptide-hyaluronan interactions. Instea d, nonspecific aggregation of the peptides with link protein is propos ed to account for all of the experimental data. Consequently, there is no direct experimental evidence to support the conclusion that these sequences in the tandem repeats of link protein are responsible for th e link protein-hyaluronan interaction. If these peptides do represent the hyaluronan binding regions of link protein, these results imply a highly structure-dependent interaction between link protein and hyalur onan. Conformational analysis of the peptides using two-dimensional nu clear Overhauser spectroscopy indicates that the linear peptides do no t adopt any stable secondary structure. However, several residues in t he disulfide-looped peptides exhibit connectivities, suggesting a rela tively long-lived extended chain conformation, consistent with predict ions of secondary structure based on sequence analysis.