Crystal structure and conformation of L-pyroglutamyl-L-alanine.
Crystals of the dipeptide, pyroglutamyl-alanine (C8H12N2O4) grown from aqueous methanol are monoclinic, space group P2(1) with the following cell parameters: a = 4.863(2), b = 16.069(1), c = 6.534(2)A and beta = 109.9(2) degrees, V = 480.0A3, Mr = 200.2, Dc = 1.385 g cm-3, and Z = 2. The crystal structure was solved by the application of direct methods and refined to an R value of 0.044 for 699 reflections with I greater than 2 sigma. The amide of the pyroglutamyl side chain is cis, omega 1 = 2.6(7) degrees; the peptide unit is trans and appreciably non-planar (omega 2 = 167.4(5) degrees). The backbone torsional angles are: psi 1 = 166.1(5), phi 2 = -90.3(6), and psi 2 = -22.4(6) degrees. This structure contains a short (2.551(5)A) intermolecular hydrogen bond between the carboxyl OH and the N-acyl oxygen, a feature common to most acyl amino acids and acyl peptides.
Ramasubbu
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Center for Crystallographic Research, Roswell Park Memorial Institute, Buffalo, NY.
Parthasarathy
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D055598:Chemical Phenomena; D002621:Chemistry; D003461:Crystallography; D004151:Dipeptides / Q000032:analysis*; D006860:Hydrogen Bonding; D011487:Protein Conformation; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D012984:Software
D004151:Dipeptides; C060738:L-pyroglutamyl-L-alanine; D011761:Pyrrolidonecarboxylic Acid