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X Q Ma

Publications and source records attributed to X Q Ma.

6 recordsLinked to original sources
PubMed1994

Refined structure of trichosanthin at 1.73 A resolution.

An X-ray reflection data set of the orthorhombic crystal of Trichosanthin (TCS) at 1.73 A resolution had been collected using the area detector. We determined TCS crystal structure by the molecular replacement method using the data of the known alpha-momocharin model and TCS intensities, and then TCS structure refinement at 1.73 A resolution was performed with the restrained least-squares refinement. A final R-factor of 0.186 was obtained with a model obeying standard geometry within 0.013 A in bond lengths and 2.48 degrees in bond angles. The final model contains 133 solvent molecules in the asymmetric unit. This paper gives a detailed description of TCS molecule structure, temperature factors, hydrogen bonds, bound water, the distribution of conserved residues and the interactions between the TCS molecules. The hydrogen bond between the hydroxyl group of conserved residue 14Tyr and O157 plays an important role in maintaining the active site conformation. Conserved residue 160Glu and its conformation at the active site play a key role in the catalytic activity.

Crystallography, X-Ray↗
PubMed1990

Crystal structure of a protein-toxin alpha 1-purothionin at 2.5A and a comparison with predicted models.

Alpha 1-Purothionin (alpha 1-P), a wheatgerm protein and lytic toxin, has a secondary and tertiary structure similar to that of crambin as revealed by CD and NMR studies. alpha 1-P crystallizes in the tetragonal space group 1422 with unit cell dimensions: a = b = 53.59 and c = 69.79 A. X-ray diffraction data have been measured to 2.5 A Bragg spacing. The crystal structure has been determined by molecular replacement methods, using an energy-minimized alpha 1-P model structure derived from crambin (Whitlow and Teeter: Journal of Biomolecular Structure and Dynamics 2:831-848, 1985, Journal of the American Chemical Society 108:7163-7172, 1986). The energy-minimized model gives a slightly cleaner rotation solution and better refinement against the x-ray data than do the crambin or unminimized alpha 1-P structures. The final crystallographic residual with the data in the 10-2.5 A resolution range is 0.216. The refined alpha 1-P structure has a backbone rms difference of 0.74 A from crambin and 0.55 A from the energy-minimized alpha 1-P model. A low resolution NMR model of alpha 1-P calculated from metric matrix distance geometry and restrained molecular dynamics differs from crambin's backbone by 2.3 A rms deviation (Clore et al.: EMBO Journal 5:2729-2735, 1986). Backbone dihedral angles for our predicted model differ from the refined alpha 1-P structure in only one region (at a turn where there is a deletion relative to crambin). The NMR model had differences in four regions.

Antimicrobial Cationic Peptides↗
PubMed1987

An X-ray analysis of the orthorhombic crystal form of trichosanthin at 5 angstrom.

Trichosanthin crystals grown at pH 5.4 are orthorhombic P212121 with cell dimension a = 38.23 angstrom, b = 76.18 angstrom and c = 79.12 angstrom. Each asymmetric unit contains one protein molecule of 234 amino acid residues (M. W. 26,000). The structure has been solved at 5 angstrom resolution by conventional MIR method with two heavy-atom derivatives. The preliminary result suggests that the protein molecule in acidic solution does not have dramatic conformational change, compared with that in alkali solution.

Abortifacient Agents↗
PubMed1987

The three-dimensional structure of trichosanthin molecule.

A model completed recently of two trichosanthin molecules in an asymmetric unit belonging to the monoclinic system is reported. It can be seen that the molecular structure consists of two domains, one large and one small, and that there are some features in the secondary structure. The dissimilarity between two molecules as well as their interactions in an independent unit correlated in a non-symmetric way has been described, moreover, the binding sites of the heavyatom position in the derivatives are also discussed.

Abortifacient Agents↗