Peptide crystal growth via vapor diffusion. Crystal structure of glycyl-L-tyrosyl-L-alanine dihydrate.

The structure of a dihydrated form of glycyl-L-tyrosyl-L-alanine (GYA) has been determined as part of a series of peptide structural investigations and development of microscale vapor diffusion experiments for peptide crystal growth. Crystals were grown by the hanging-drop method against sodium acetate. The tripeptide is a zwitterion in the crystal, adopting an extended conformation through glycine, a nearly perpendicular bend attyrosine and a reverse turn for the C-terminal carboxylate. Principal backbone torsion angles are ψ1 175(1)°, ω2 173(1)°, φ2 -119(1)°, ψ2 120(1)°, ω33 172(1)°, φ3 -73(1)°,ψ31 -9(1)°, ψ32 171(1)°. The tyrosyl side chain adopts an unusual orientation (χ1/2= -86(1)°). The relationship of the GYA.2H2O structure to GYA sequences in proteins is examined, particularly as regards its helix-forming potential. Crystal data: C14H19N3O4.2H2O, Mr = 345.36, orthorhombic, P212121, a = 4.810 (4), b= 11.400(7), c = 30.162(23)A, V=1653.8(24)A−3, Z = 4, Dx= 1.387 Mgm−3, λ(CuKα−)= 1.540 Aμ= 9.053 mm−1, F(000) = 736, T = 199K, R = 0.041 for 1458 observations with I ≥ 3σ(I).