A comparison of the structures of apo dogfish M4 lactate dehydrogenase and its ternary complexes |
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Authors: | Janice L White Marvin L Hackert Manfred Buehner Margaret J Adams Geoffrey C Ford Paul J Lentz Ira E Smiley Steven J Steindel Michael G Rossmann |
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Institution: | Department of Biological Sciences, Purdue University West Lafayette, Ind. 47907, U.S.A. |
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Abstract: | Details are recorded of the X-ray diffraction data collection, heavy atom refinement and preliminary structure refinement for two different dogfish M4 lactate dehydrogenase structures. One of these is the 2.0 Å resolution apoenzyme structure; the other is a 3.0 Å resolution abortive ternary complex. Two other ternary substrate inhibitory complexes (LDHase2: NAD: oxalate and LDHase: NADH: oxamate), isomorphous with the abortive ternary complex (LDHase: NAD-pyruvate), have also been examined. The apo-LDHase and LDHase: NAD-pyruvate structures are systematically compared to determine significant differences in their conformation. These are related to differences in structure amongst the three studied ternary complexes. These differences all occur in regions of the protein around the active site, particularly the flexible loop covering the active center pocket and the C-terminal helix αH. The changes are suggestive of a domino effect whereby the closing of the loop on binding coenzyme and substrate triggers the critical reactive residues into assuming their catalytically active positions. |
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