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Functional differentiation of antiporter-like polypeptides in complex I; a site-directed mutagenesis study of residues conserved in MrpA and NuoL but Not in MrpD, NuoM, and NuoN

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Author

  • Eva Sperling
  • Kamil Górecki
  • Torbjörn Drakenberg
  • Cecilia Hägerhäll

Summary, in English

It has long been known that the three largest subunits in the membrane domain (NuoL, NuoM and NuoN) of complex I are homologous to each other, as well as to two subunits (MrpA and MrpD) from a Na+ /H+ antiporter, Mrp. MrpA and NuoL are more similar to each other and the same is true for MrpD and NuoN. This suggests a functional differentiation which was proven experimentally in a deletion strain model system, where NuoL could restore the loss of MrpA, but not that of MrpD and vice versa. The simplest explanation for these observations was that the MrpA and MrpD proteins are not antiporters, but rather single subunit ion channels that together form an antiporter. In this work our focus was on a set of amino acid residues in helix VIII, which are only conserved in NuoL and MrpA (but not in any of the other antiporter-like subunits.) and to compare their effect on the function of these two proteins. By combining complementation studies in B. subtilis and 23Na-NMR, response of mutants to high sodium levels were tested. All of the mutants were able to cope with high salt levels; however, all but one mutation (M258I/M225I) showed differences in the efficiency of cell growth and sodium efflux. Our findings showed that, although very similar in sequence, NuoL and MrpA seem to differ on the functional level. Nonetheless the studied mutations gave rise to interesting phenotypes which are of interest in complex I research.

Publishing year

2016-07-01

Language

English

Publication/Series

PLoS ONE

Volume

11

Issue

7

Document type

Journal article

Publisher

Public Library of Science (PLoS)

Topic

  • Biochemistry and Molecular Biology
  • Structural Biology

Status

Published

Research group

  • Medical Structural Biology

ISBN/ISSN/Other

  • ISSN: 1932-6203