1. 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
G S Padiyar J Pept Res. 1998 Apr;51(4):266-70. doi: 10.1111/j.1399-3011.1998.tb00423.x.
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.
2. Synthetic peptide derivatives that bind to fibrinogen and prevent the polymerization of fibrin monomers
A P Laudano, R F Doolittle Proc Natl Acad Sci U S A. 1978 Jul;75(7):3085-9. doi: 10.1073/pnas.75.7.3085.
A series of small peptides corresponding to the amino termini of the fibrin alpha- and beta-chains has been synthesized. The peptides glycyl-L-prolyl-L-arginyl-L-proline and glycyl-L-prolyl-L-arginylsarcosine are potent inhibitors of fibrin polymerization. Moreover, these peptides have a natural stability stemming from their inherent resistance to proteolysis because of the involvement of amino acids in each of their peptide bonds. The peptide glycyl-L-prolyl-L-arginyl-L-proline binds to fibrinogen and to fragment D, in both cases with an association constant of approximately 5 x 10(4); it does not bind to fragment E. The number of binding sites is two for fibrinogen and one for fragment D. The tripeptide glycyl-L-prolyl-L-arginine binds less tightly and is less than half as effective in preventing polymerization. The peptide glycyl-L-histidyl-L-arginyl-L-proline, which corresponds exactly to the amino terminus of the fibrin beta-chain, does not inhibit the aggregation of fibrin monomers under the conditions used. It does bind weakly to fibrinogen, however, suggesting the involvement of sites other than those binding the alpha-chain analogues. Various other peptides were found not to inhibit polymerization; these included glycine-L-proline, L-prolyl-L-arginine and glycyl-L-prolyl-L-seryl-L-proline. The last-named corresponds to the serine/arginine amino acid replacement previously reported for a defective human fibrinogen.
3. L-histidyl-L-serine 3.7-hydrate: water channels in the crystal structure of a polar dipeptide
Carl Henrik Görbitz Acta Crystallogr C. 2010 Nov;66(Pt 11):o531-4. doi: 10.1107/S0108270110038254. Epub 2010 Oct 8.
Dipeptides may form nanotubular structures with pore diameters in the range 3.2-10 Å. These compounds normally contain at least one and usually two hydrophobic residues, but L-His-L-Ser hydrate, C(9)H(14)N(4)O(4)·3.7H(2)O, with two hydrophilic residues, forms large polar channels filled with ordered as well as disordered water molecules.
