Crystal structure and conformation of polypeptides: L-leucylglycylglycylglycine.
Crystals of L-leucylglycylglycylglycine, LGGG (C12H22N4O5), grown from an ethanol-water solution, are orthorhombic, space groups P2(1)2(1)2(1), with unit cell dimensions (at 22 +/- 3 degrees) a = 9.337(1), b = 10.995(1), c = 15.235(1)A, v = 1563.4 A3, Z = 4 with a density of Dobs = 1.29 g.cm-3 and Dcalc = 1.279 g.cm-3. The crystal structure was solved by the application of direct methods and refined to an R value of 0.029 for 1018 reflections with I greater than or equal to 2 sigma. The molecule exists as a zwitterion in the crystal. The trans peptide backbone takes up a folded conformation at the middle glycylglycyl link accompanied by a significant nonplanarity up to delta omega of 8 degrees at the middle peptide and is relatively more extended at the two ends. The molecules are linked together intermolecularly in an infinite sequence of head to tail 1-4' hydrogen bonds, as is typical of charged peptides. It is interesting to note that while glycylglycylglycine takes up an extended beta-sheet conformation, addition of Leu to the N-terminal results in a bent conformation.
Srikrishnan
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Center for Crystallographic Research, Roswell Park Memorial Institute, Buffalo, New York.
Parthasarathy
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D003460:Crystallization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009842:Oligopeptides; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
D009842:Oligopeptides; C021050:leucyl-glycyl-glycyl-glycine