An apolar synthetic analog of the first 10 residues at the NH2-terminal end of zervamicin HA crystallizes in the triclinic space group P1 with cell dimensions a = 10.206 ± 0.002 A, b = 12.244 ± 0.002 A, c = 15.049 ± 0.002 A, α = 93.94 ± 0.01°, β = 95.10 ± 0.01°, γ = 104.56 ± 0.01°, Z = 1, C60H97N1103.2H2O. Despite the relatively few a-aminoisobutyric acid residues, the peptide maintains a helical form. The first intrahelical hydrogen bond is of the 310 type between N(3) and 0(0), followed by five α-helix-type hydrogen bonds. Solution 1H NMR studies in chloroform also favor a helical conformation, with seven solvent-shielded NH groups. Continuous columns are formed by head-to-tail hydrogen bonds between the helical molecules along the helix axis. The absence of polar side chains precludes any lateral hydrogen bonds. Since the peptide crystallizes with one molecule in a trilinic space group, aggregation of the helical columns must necessarily be parallel rather than antiparallel. The packdng of the columns is rather inefficient, as indicated by very few good van der Waals' contacts and the occurrence of voids between the molecules
