HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Scott, J. D. Articles by Ludwig, R. A. Search for Related Content PubMed PubMed Citation Articles by Scott, J. D. Articles by Ludwig, R. A. Agricola Articles by Scott, J. D. Articles by Ludwig, R. A.

Azorhizobium caulinodans electron-transferring flavoprotein N electrochemically couples pyruvate dehydrogenase complex activity to N₂ fixation

Department of Molecular, Cellular and Developmental Biology, Sinsheimer Laboratories, University of California, Santa Cruz, CA 95064, USA

Correspondence
Robert A. Ludwig
ludwig{at}biology.ucsc.edu

Azorhizobium caulinodans thermolabile point mutants unable to fix N₂ at 42 °C were isolated and mapped to three, unlinked loci; from complementation tests, several mutants were assigned to the fixABCX locus. Of these, two independent fixB mutants carried missense substitutions in the product electron-transferring flavoprotein N (ETF_N) -subunit. Both thermolabile missense variants Y238H and D229G mapped to the ETF_N interdomain linker. Unlinked thermostable suppressors of these two fixB missense mutants were identified and mapped to the lpdA gene, encoding dihydrolipoamide dehydrogenase (LpDH), immediately distal to the pdhABC genes, which collectively encode the pyruvate dehydrogenase (PDH) complex. These two suppressor alleles encoded LpDH NAD-binding domain missense mutants G187S and E210G. Crude cell extracts of these fixB lpdA double mutants showed 60–70 % of the wild-type PDH activity; neither fixB lpdA double mutant strain exhibited any growth phenotype at the restrictive or the permissive temperature. The genetic interaction between two combinations of lpdA and fixB missense alleles implies a physical interaction of their respective products, LpDH and ETF_N. Presumably, this interaction electrochemically couples LpDH as the electron donor to ETF_N as the electron acceptor, allowing PDH complex activity (pyruvate oxidation) to drive soluble electron transport via ETF_N to N₂, which acts as the terminal electron acceptor. If so, then, the A. caulinodans PDH complex activity sustains N₂ fixation both as the driving force for oxidative phosphorylation and as the metabolic electron donor.

The nucleotide sequence for the Azorhizobium caulinodans dihydrolipoamide dehydrogenase gene (lpdA) described in this article has been deposited in GenBank under accession number AY331184.

This article has been cited by other articles:

				M. J. Mitsch, A. Cowie, and T. M. Finan Malic Enzyme Cofactor and Domain Requirements for Symbiotic N2 Fixation by Sinorhizobium meliloti J. Bacteriol., January 1, 2007; 189(1): 160 - 168. [Abstract] [Full Text] [PDF]