Previous studies showed that chromogranin A (CgA), a glycoprotein stored and co-released with various hormones by neuroendocrine cells and neurons, can modulate cell adhesion. We have investigated the structureactivity relationships of CgA using fibroblasts and coronary artery smooth muscle cells in adhesion assays. A recombinant CgA fragment 1-78 and a peptide 7-57 containing reduced and alkylated cysteines (Cys 17 and Cys 38 ) induced cell adhesion after adsorption onto solid phases at 50 -100 nM. Peptides lacking the disulfide loop region, including residues 47-68, 39 -59, and 39 -68, induced cell adhesion, either bound to solid phases at 200 -400 nM or added to the liquid phase at 5-10 M, whereas peptide 60 -68 was inactive, suggesting that residues 47-57 are important for activity. The effect of CgA-(1-78) was blocked by anti-CgA antibodies against epitopes including residues Arg 53 , His 54 , and Leu 57 . Substitutions of residues His 54 , Gln 55 , and Asn 56 with alanine decreased the cell adhesion activity of peptide 47-68. These results suggest that the region 47-57 (RILSILRHQNL) contains a cell adhesion site and that the disulfide bridge is not necessary for the proadhesive activity. The ability of soluble peptides to elicit proadhesive effects suggests an indirect mechanism. The high sequence conservation and accessibility to antibodies suggest that this region is important for the physiological role of CgA.

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beta-Endorphin has been studied in SDS micelles by one- and two-dimensional nmr spectroscopy (1D and 2D nmr), and to explore the influence of peptide length and composition on the polypeptide structure, the investigation was extended to a number of fragments. The nmr results are compared with those obtained from CD experiments and discussed in terms of a secondary structure that involves the central region of beta-endorphin.

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