1xcb

From Proteopedia

Revision as of 13:07, 20 March 2008

X-ray Structure of a Rex-Family Repressor/NADH Complex from Thermus Aquaticus

Overview

The redox-sensing repressor Rex regulates transcription of respiratory genes in response to the intra cellular NADH/NAD(+) redox poise. As a step toward elucidating the molecular mechanism of NADH/NAD(+) sensing, the X-ray structure of Thermus aquaticus Rex (T-Rex) bound to effector NADH has been determined at 2.9 A resolution. The fold of the C-terminal domain of T-Rex is characteristic of NAD(H)-dependent enzymes, whereas the N-terminal domain is similar to a winged helix DNA binding motif. T-Rex dimerization is primarily mediated by "domain-swapped" alpha helices. Each NADH molecule binds to the C-terminal domain near the dimer interface. In contrast to NAD(H)-dependent enzymes, the nicotinamide is deeply buried within a hydrophobic pocket that appears to preclude substrate entry. We show that T-Rex binds to the Rex operator, and NADH but not NAD(+) inhibits T-Rex/DNA binding activity. A mechanism for redox sensing by Rex family members is proposed by analogy with domain closure of NAD(H)-dependent enzymes.

About this Structure

1XCB is a Single protein structure of sequence from Thermus aquaticus. This structure supersedes the now removed PDB entry 1R72. Full crystallographic information is available from OCA.

Reference

X-ray structure of a Rex-family repressor/NADH complex insights into the mechanism of redox sensing., Sickmier EA, Brekasis D, Paranawithana S, Bonanno JB, Paget MS, Burley SK, Kielkopf CL, Structure. 2005 Jan;13(1):43-54. PMID:15642260

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