A1 Journal article – refereed
Membrane-integral pyrophosphatase subfamily capable of translocating both Na+ and H+




List of Authors: Luoto HH, Baykov AA, Lahti R, Malinen AM
Publisher: NATL ACAD SCIENCES
Publication year: 2013
Journal: Proceedings of the National Academy of Sciences of the United States of America
Journal name in source: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Journal acronym: PROC NATL ACAD SCI USA
Number in series: 4
Volume number: 110
Issue number: 4
Number of pages: 6
ISSN: 1091-6490

Abstract
One of the strategies used by organisms to adapt to life under conditions of short energy supply is to use the by-product pyrophosphate to support cation gradients in membranes. Transport reactions are catalyzed by membrane-integral pyrophosphatases (PPases), which are classified into two homologous subfamilies: H+-transporting (found in prokaryotes, protists, and plants) and Na+-transporting (found in prokaryotes). Transport activities have been believed to require specific machinery for each ion, in accordance with the prevailing paradigm in membrane transport. However, experiments using a fluorescent pH probe and Na-22(+) measurements in the current study revealed that five bacterial PPases expressed in Escherichia coli have the ability to simultaneously translocate H+ and Na+ into inverted membrane vesicles under physiological conditions. Consistent with data from phylogenetic analyses, our results support the existence of a third, dual-specificity bacterial Na+, H+-PPase subfamily, which apparently evolved from Na+-PPases. Interestingly, genes for Na+, H+-PPase have been found in the major microbes colonizing the human gastrointestinal tract. The Na+, H+-PPases require Na+ for hydrolytic and transport activities and are further activated by K+. Based on ionophore effects, we conclude that the Na+ and H+ transport reactions are electrogenic and do not result from secondary antiport effects. Sequence comparisons further disclosed four Na+, H+-PPase signature residues located outside the ion conductance channel identified earlier in PPases using X-ray crystallography. Our results collectively support the emerging paradigm that both Na+ and H+ can be transported via the same mechanism, with switching between Na+ and H+ specificities requiring only subtle changes in the transporter structure.

Last updated on 2019-20-07 at 13:58