Crystal structure and conformation of methionyl dipeptides: Structure of L-methionyl-L-asparagine: Preferred conformations of peptides containing methionyl and asparaginyl residues

Abstract

Crystals of L-methionyl-L-asparagines (C9N3H17O4S) are orthorhombic, space group P212121, with cell parameters at 294 K of a = 5.248(1), b = 13.251(2), c = 18.028(2) A, V = 1251.6(4) A3, Z = 4, Dm = 1.40 Mg/m3, and Dx = 1.397 Mg/m3. The crystal structure was solved by direct methods and refinded by full-matrix least-squares method to a final R value of 0.059 for 1804 reflections. The peptide is slightly nonpalnar [ω = 172.0(5)∘]; the other torsion angles ψ1, ϕ2, ψ21, and ψ22 are 155.6(5), −95.8(5), 152.5(5), and −29.4(6)∘ respectively. The methionyl side chain is disordered with two possible position for its Cγ, Sδ, and Ce atoms. The methionly side chain is twisted with χ1 = −86.4(7), χ2 = 177.5(9), and χ3 = 116.6(2)∘ for the major conformer A. The asparaginyl side chain is also twisted with χ1 = −76.3(5) and χ2 = 102.3(6)∘. The crystal structure is stabilized by an intermolecular network of hydrogen bonds involving the N-terminal amino group and the e-terminal amino group of asn residue as donors and the carboxyl oxygens of the C-terminal and the peptide carbonyl oxygens as acceptor atoms.