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J Biol Chem. 2003 Jun 6;278(23):21240-6. Epub 2003 Mar 21.

Structural basis for flip-flop action of thiamin pyrophosphate-dependent enzymes revealed by human pyruvate dehydrogenase.

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  • 1Biological and Physical Space Research Laboratory, National Aeronautics and Space Administration/Marshall Space Flight Center and Universities Space Research Association, Huntsville, Alabama 35812, USA.


The derivative of vitamin B1, thiamin pyrophosphate, is a cofactor of enzymes performing catalysis in pathways of energy production. In alpha2beta2-heterotetrameric human pyruvate dehydrogenase, this cofactor is used to cleave the Calpha-C(=O) bond of pyruvate followed by reductive acetyl transfer to lipoyl-dihydrolipoamide acetyltransferase. The dynamic nonequivalence of two, otherwise chemically equivalent, catalytic sites has not yet been understood. To understand the mechanism of action of this enzyme, we determined the crystal structure of the holo-form of human pyruvate dehydrogenase at 1.95-A resolution. We propose a model for the flip-flop action of this enzyme through a concerted approximately 2-A shuttle-like motion of its heterodimers. Similarity of thiamin pyrophosphate binding in human pyruvate dehydrogenase with functionally related enzymes suggests that this newly defined shuttle-like motion of domains is common to the family of thiamin pyrophosphate-dependent enzymes.

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