ATOMIC-STRUCTURE OF THE CUBIC CORE OF THE PYRUVATE-DEHYDROGENASE MULTIENZYME COMPLEX

The highly symmetric pyruvate dehydrogenase multienzyme complexes have molecular masses ranging from 5 to 10 million daltons. They consist of numerous copies of three different enzymes: pyruvate dehydrogenase, dihydrolipoyl transacetylase, and lipoamide dehydrogenase. The three-dimensional crystal structure of the catalytic domain of Azotobacter vinelandii dihydrolipoyl transacetylase has been determined at 2.6 angstrom (angstrom) resolution. Eight trimers assemble as a hollow truncated cube with an edge of 125 angstrom, forming the core of the multienzyme complex. Coenzyme A must enter the 29 angstrom long active site channel from the inside of the cube, and lipoamide must enter from the outside. The trimer of the catalytic domain of dihydrolipoyl transacetylase has a topology identical to chloramphenicol acetyl transferase. The atomic structure of the 24-subunit cubic core provides a framework for understanding all pyruvate dehydrogenase and related multienzyme complexes.