1v1m

From Proteopedia

Revision as of 12:01, 5 November 2007

CROSSTALK BETWEEN COFACTOR BINDING AND THE PHOSPHORYLATION LOOP CONFORMATION IN THE BCKD MACHINE

Overview

The decarboxylase/dehydrogenase (E1b) component of the 4-megadalton human, branched-chain alpha-keto acid dehydrogenase (BCKD) metabolic machine is a, thiamin diphosphate (ThDP)-dependent enzyme with a heterotetrameric, cofactor-binding fold. The E1b component catalyzes the decarboxylation of, alpha-keto acids and the subsequent reductive acylation of the lipoic, acid-bearing domain (LBD) from the 24-meric transacylase (E2b) core. In, the present study, we show that the binding of cofactor ThDP to the E1b, active site induces a disorder-to-order transition of the conserved, phosphorylation loop carrying the two phosphorylation sites Ser(292)-alpha, and Ser(302)-alpha, as deduced from the 1.80-1.85 A apoE1b and holoE1b, structures. The induced loop conformation is essential for the recognition, of lipoylated LBD to initiate E1b-catalyzed reductive acylation., Alterations of invariant Arg(287)-alpha, Asp(295)-alpha, Tyr(300)-alpha, and Arg(301)-alpha that form a hydrogen-bonding network in the, phosphorylation loop result in the disordering of the loop conformation as, elucidated by limited proteolysis, accompanied by the impaired binding and, diminished reductive acylation of lipoylated LBD. In contrast, k(cat), values for E1b-catalyzed decarboxylation of the alpha-keto acid are higher, in these E1b mutants than in wild-type E1b, with higher K(m) values for, the substrate in the mutants. ThDP binding that orders the loop prevents, phosphorylation of E1b by the BCKD kinase and averts the inactivation of, wild-type E1b, but not the above mutants, by this covalent modification., Our results establish that the cross-talk between the bound ThDP and the, phosphorylation loop conformation serves as a feed-forward switch for, multiple reaction steps in the BCKD metabolic machine.

About this Structure

1V1M is a Protein complex structure of sequences from Homo sapiens with CL, K, MN, TDP, BEN and GOL as ligands. Active as 3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring), with EC number 1.2.4.4 Structure known Active Site: AC1. Full crystallographic information is available from OCA.

Reference

Cross-talk between thiamin diphosphate binding and phosphorylation loop conformation in human branched-chain alpha-keto acid decarboxylase/dehydrogenase., Li J, Wynn RM, Machius M, Chuang JL, Karthikeyan S, Tomchick DR, Chuang DT, J Biol Chem. 2004 Jul 30;279(31):32968-78. Epub 2004 May 27. PMID:15166214

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