Crystal structures alanine

Fig. 2.11 Preferential conformations around the C(a)-C(/9) bond in the crystal structures of /9-alanine-containing peptides [158]...

Hardness data for only two amino acids were found in the literature. They are glycine and alanine. They are the smallest of the amino acids. Both consist of rather flat tablet-like collections of atoms that form layered crystal structures in which the molecular sub-groups within the layers are held together by hydrogen bonds (Albrecht and Corey, 1939), and the molecules by London forces. Their hardnesses are ... 

One of the important consequences of studying catalysis by mutant enzymes in comparison with wild-type enzymes is the possibility of identifying residues involved in catalysis that are not apparent from crystal structure determinations. This has been usefully applied (Fersht et al., 1988) to the tyrosine activation step in tyrosine tRNA synthetase (47) and (49). The residues Lys-82, Arg-86, Lys-230 and Lys-233 were replaced by alanine. Each mutation was studied in turn, and comparison with the wild-type enzyme revealed that each mutant was substantially less effective in catalysing formation of tyrosyl adenylate. Kinetic studies showed that these residues interact with the transition state for formation of tyrosyl adenylate and pyrophosphate from tyrosine and ATP and have relatively minor effects on the binding of tyrosine and tyrosyl adenylate. However, the crystal structures of the tyrosine-enzyme complex (Brick and Blow, 1987) and tyrosyl adenylate complex (Rubin and Blow, 1981) show that the residues Lys-82 and Arg-86 are on one side of the substrate-binding site and Lys-230 and Lys-233 are on the opposite side. It would be concluded from the crystal structures that not all four residues could be simultaneously involved in the catalytic process. Movement of one pair of residues close to the substrate moves the other pair of residues away. It is therefore concluded from the kinetic effects observed for the mutants that, in the wild-type enzyme, formation of the transition state for the reaction involves a conformational change to a structure which differs from the enzyme structure in the complex with tyrosine or tyrosine adenylate. The induced fit to the transition-state structure must allow interaction with all four residues simultaneously. 

FIGURE 1.19 X-ray crystal structures of selector-selectand complexes (ion-pairs) (a) O-9-(P-chloro-fert-butylcarbamoyl)quinine with iV-(3,5-dinitrobenzoyl)-(5)-leucine, (b) tbe pseudoenantiomeric complex of 0-9-( 3-cbloro-tert-butylcarbamoyl)quinidine with N-(3,5-dinitrobenzoyl)-(i )-leucine, (c) 0-9-( 3-cbloro-terf-butylcarbamoyl)quinine with N-(3,5-dinitrobenzoyl)-(5)-alanyl-(5)-alanine, and (d) comparison of tbe complexes of (a) and (c). Most hydrogens have been omitted for the purpose of clarity. (Reprinted from C. Czerwenka et al., Anal. Chem., 74 5658 (2002). With permission.)... 

Kim s group in Seoul report the application of another of the E. coli ATs, the aromatic l-AAT encoded by the tyrB gene, to enrich the D-component of racemic preparations of alanine substituted at the /3-position with pyrazole, triazole, and imidazole. They also carried out an in silico investigation based on the crystal structure (PDB 3TAT) providing a reasonable rationalization (and therefore also potentially prediction) of substrate specificities. 

LeMagueres, R Im, H. Dvorak, A. Strych, U. Benedik, M. Krause, K. L. Crystal Structure at 1.45 A Resolution of Alanine Racemase from a Pathogenic Bacterium, Pseudomonas aeruginosa, Contains Both Internal and External Aldimine Forms. Biochemistry 2003, 42, 14752-14761. 

Structure of the lithio derivatives (84CC853) The crystal structure of a THF solvate of the lithium derivative of racemic bislactim ether (derived from two molecules of alanine) has been determined. In the solid state, the lithium derivative exists as a dimer in which the two lithium atoms are nonequivalent (189). The two organic moieties in each dimer are homo-chiral this means that the crystal contains equal number of enantiomers. The Li Li distance is 2.61 A. In THF solution at - 108°C, the compound seems to exist as an equilibrium mixture of monomer and dimer in the ratio 5 1. It is not clear at the moment whether the reacting species is the monomer or the dimer. 

A crystal structure of the all-tram isomer of [Cr2(gly)4(OH)2] has been reported.1162 Its low temperature magnetic susceptibility has been fitted to both the Van Vleck and modified Van Vleck models. The uncorrected model leads to, uef = 3.80BM with 2/= 8.4 cm-1 1162,1163,1164 with the inclusion of quadratic exchange 2/=7.4 cm-1.1162 Related studies of alanine,1153,1163 valine, phenylalanine, leucine,1163,1149 proline1166,1167 and histidine1168 complexes have appeared. The proline complex is unusual in that it is soluble in methanol and DMSO. Circular dichroism spectra have been measured the X-ray structure shows the complex to be the L-bms(N), L-tram(0) isomer.1166 More complicated dimers of unusual stoichiometry have been reported.1169... 

The crystal structure of the N-terminal 80 residues of tropomyosin (Brown et al., 2001) contains its first alanine cluster and displays two specific consequences of this motif for the main-chain geometry of the coiled-coil. One is that the coiled-coil in this segment becomes locally narrow, to 8.0 A diameter, as would be expected from alanine s small size. This feature is directly related to the stability of the coiled-coil in a 10 A wide dimeric coiled-coil, a pair of core alanines from the opposite helices would generally leave unfilled spaces in the interior these spaces become smaller as the main chains of the helices approach each other and the core becomes more close-packed. Recent studies of model coiled-coils with identical amino acid compositions, but different arrangements,... 

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