1u2d
From Proteopedia
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Structre of transhydrogenaes (dI.NADH)2(dIII.NADPH)1 asymmetric complex
Overview
Transhydrogenase couples the redox (hydride-transfer) reaction between, NAD(H) and NADP(H) to proton translocation across a membrane. The redox, reaction is catalyzed at the interface between two components (dI and, dIII) which protrude from the membrane. A complex formed from recombinant, dI and dIII (the dI(2)dIII(1) complex) from Rhodospirillum rubrum, transhydrogenase catalyzes fast single-turnover hydride transfer between, bound nucleotides. In this report we describe three new crystal structures, of the dI(2)dIII(1) complex in different nucleotide-bound forms. The, structures reveal an asymmetry in nucleotide binding that complements, results from solution studies and supports the notion that intact, transhydrogenase functions by an alternating site mechanism. In one, structure, the redox site is occupied by NADH (on dI) and NADPH (on dIII)., The dihydronicotinamide rings take up positions which may approximate to, the ground state for hydride transfer: the redox-active C4(N) atoms are, separated by only 3.6 A, and the perceived reaction stereochemistry, matches that observed experimentally. The NADH conformation is different, in the two dI polypeptides of this form of the dI(2)dIII(1) complex., Comparisons between a number of X-ray structures show that a, conformational change in the NADH is driven by relative movement of the, two domains which comprise dI. It is suggested that an equivalent, conformational change in the intact enzyme is important in gating the, hydride-transfer reaction. The observed nucleotide conformational change, in the dI(2)dIII(1) complex is accompanied by rearrangements in the, orientation of local amino acid side chains which may be responsible for, sealing the site from the solvent and polarizing hydride transfer.
About this Structure
1U2D is a Protein complex structure of sequences from Rhodospirillum rubrum with NAD, NDP and GOL as ligands. Active as NAD(P)(+) transhydrogenase (AB-specific), with EC number 1.6.1.2 Full crystallographic information is available from OCA.
Reference
Active-site conformational changes associated with hydride transfer in proton-translocating transhydrogenase., Mather OC, Singh A, van Boxel GI, White SA, Jackson JB, Biochemistry. 2004 Aug 31;43(34):10952-64. PMID:15323555
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