Promotion of cell adhesion by single-stranded and triple-helical peptide models of basement membrane collagen α1-(IV)531-543: Evidence for conformationally dependent and conformationally independent type IV collagen cell adhesion sites

Several regions within the triple-helical domain of type IV collagen function as cellular recognition sites. We have demonstrated previously that melanoma cell activities promoted by the α1(IV)1263-1277 sequence are enhanced by triple helicity (Fields, C. G., Mickelson, D. J., Drake, S. L., McCarthy, J. B., and Fields, G. B. (1993) J. Biol. Chem. 268, 14153-14160), whereas Eble et al. reached similar conclusions for α1β1 integrin-mediated fibrosarcoma cell adhesion to [α1(IV)]₂α2(IV)434-472 (Eble, J. A., Golbik, R., Mann, K., and Kühn, K. (1993) EMBO J. 12, 4795-4802). In the present study, we have examined the cell adhesion activities of a third region in type IV collagen. A single-stranded peptide (SSP) incorporating the α1(IV)531-543 sequence promoted the adhesion of melanoma, ovarian carcinoma, and Jurkat cells in a dose-dependent manner, with 40% cell adhesion observed at [SSP] = 1.8, 11.5, and 42.2 UM, respectively. Nearly identical results were obtained for cell adhesion to an all-D-enantiomer of the SSP, suggesting that the cell surface receptor(s) for this site do not discriminate based on chirality. The α1(IV)531-543 sequence maintained its cell adhesion promoting activity when incorporated into a homotrimeric triple-helical polypeptide, although relative levels of adhesion were either slightly enhanced or slightly diminished compared with the SSP. Triple-helical conformation was thus not critical for cellular recognition of the α1(IV)531-543 sequence. Single-site substitution experiments of the SSP showed no overall correlation between the biological effects of substitutions and SSP conformation. The SSP, D-SSP, triple-helical polypeptide, and SSP substitution results suggest that cell recognition of the α1(IV)531-543 sequence is generally independent of substrate conformation. The present and prior studies indicate that "conformationally dependent" and "conformationally independent" cellular recognition sites exist within the triple-helical domain of type IV collagen.