1. Direct evidence for the size and conformational variability of the pyruvate dehydrogenase complex revealed by three-dimensional electron microscopy. The "breathing" core and its functional relationship to protein dynamics.
- Author
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Zhou ZH, Liao W, Cheng RH, Lawson JE, McCarthy DB, Reed LJ, and Stoops JK
- Subjects
- Binding Sites, Dihydrolipoyllysine-Residue Acetyltransferase, Geobacillus stearothermophilus enzymology, Image Processing, Computer-Assisted, Microscopy, Electron, Models, Molecular, Protein Conformation, Protein Structure, Secondary, Protein Subunits, Saccharomyces cerevisiae enzymology, Saccharomyces cerevisiae Proteins, Acetyltransferases chemistry, Acetyltransferases ultrastructure, Pyruvate Dehydrogenase Complex chemistry, Pyruvate Dehydrogenase Complex ultrastructure
- Abstract
Structural studies by three-dimensional electron microscopy of the Saccharomyces cerevisiae truncated dihydrolipoamide acetyltransferase (tE(2)) component of the pyruvate dehydrogenase complex reveal an extraordinary example of protein dynamics. The tE(2) forms a 60-subunit core with the morphology of a pentagonal dodecahedron and consists of 20 cone-shaped trimers interconnected by 30 bridges. Frozen-hydrated and stained molecules of tE(2) in the same field vary in size approximately 20%. Analyses of the data show that the size distribution is bell-shaped, and there is an approximately 40-A difference in the diameter of the smallest and largest structures that corresponds to approximately 14 A of variation in the length of the bridge between interconnected trimers. Companion studies of mature E(2) show that the complex of the intact subunit exhibits a similar size variation. The x-ray structure of Bacillus stearothermophilus tE(2) shows that there is an approximately 10-A gap between adjacent trimers and that the trimers are interconnected by the potentially flexible C-terminal ends of two adjacent subunits. We propose that this springlike feature is involved in a thermally driven expansion and contraction of the core and, since it appears to be a common feature in the phylogeny of pyruvate dehydrogenase complexes, protein dynamics is an integral component of the function of these multienzyme complexes.
- Published
- 2001
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