title: Crystal and molecular structure of L-histidyl-L-serine trihydrate: occurrence of C(alpha)-H...O=C hydrogen bond motif similar to the motif in collagen triple helix and beta-sheets.
abstract: L-Histidyl-L-serine (HSN) trihydrate, C9H14N4O4-H2O, crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 4.865(4), b = 15.604(4), c = 18.918(5) and Z = 4. The crystal structure was solved by direct methods and refined to R1 = 0.070 by a full-matrix least-squares method. The peptide exists in a zwitterionic form, with the N-terminus in a protonated form and the C-terminus in an ionized form. The imidazole ring of histidine in its neutral His(epsilon) tautomeric state has conformational angles chi(1)2 of -53.5(7) degrees and chi(21)1 of -55.4(8) degrees and the serine hydroxyl group has chi(1)2 of 68.2(7) degrees. The conformational angles deviate significantly from those of the dipeptide complexed with glycyl-L-glutamic acid in which the histidine is protonated. A noteworthy feature of the crystal packing is the occurrence of a C(alpha)-H O=C hydrogen bond motif similar to that observed in collagen triple helix and beta-sheets.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore. gspadiya@physics.iisc.ernet.in
authors.forename: G S
authors.initials: GS
authors.lastname: Padiyar
mesh_terms: D000818:Animals; D003094:Collagen / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry; D006801:Humans; D006859:Hydrogen; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D012694:Serine / Q000737:chemistry
chemical_list: D010455:Peptides; D012694:Serine; D006639:Histidine; D006859:Hydrogen; D003094:Collagen