Document Detail


An extremely halophilic proteobacterium combines a highly acidic proteome with a low cytoplasmic potassium content.
MedLine Citation:
PMID:  23144460     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Halophilic archaea accumulate molar concentrations of KCl in their cytoplasm as an osmoprotectant and have evolved highly acidic proteomes that function only at high salinity. We examined osmoprotection in the photosynthetic Proteobacteria Halorhodospira halophila and Halorhodospira halochloris. Genome sequencing and isoelectric focusing gel electrophoresis showed that the proteome of H. halophila is acidic. In line with this finding, H. halophila accumulated molar concentrations of KCl when grown in high salt medium as detected by x-ray microanalysis and plasma emission spectrometry. This result extends the taxonomic range of organisms using KCl as a main osmoprotectant to the Proteobacteria. The closely related organism H. halochloris does not exhibit an acidic proteome, matching its inability to accumulate K(+). This observation indicates recent evolutionary changes in the osmoprotection strategy of these organisms. Upon growth of H. halophila in low salt medium, its cytoplasmic K(+) content matches that of Escherichia coli, revealing an acidic proteome that can function in the absence of high cytoplasmic salt concentrations. These findings necessitate a reassessment of two central aspects of theories for understanding extreme halophiles. First, we conclude that proteome acidity is not driven by stabilizing interactions between K(+) ions and acidic side chains but by the need for maintaining sufficient solvation and hydration of the protein surface at high salinity through strongly hydrated carboxylates. Second, we propose that obligate protein halophilicity is a non-adaptive property resulting from genetic drift in which constructive neutral evolution progressively incorporates weakly stabilizing K(+)-binding sites on an increasingly acidic protein surface.
Authors:
Ratnakar Deole; Jean Challacombe; Douglas W Raiford; Wouter D Hoff
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2012-11-09
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  288     ISSN:  1083-351X     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-01-07     Completed Date:  2013-02-28     Revised Date:  2014-01-09    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  581-8     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
Archaea / metabolism
Archaeal Proteins / metabolism
Binding Sites
Computational Biology / methods
Cytoplasm / metabolism*
Dose-Response Relationship, Drug
Ectothiorhodospiraceae / metabolism
Electrons
Evolution, Molecular
Genomics
Ions
Isoelectric Focusing
Models, Genetic
Potassium / chemistry,  metabolism*
Potassium Chloride / chemistry
Proteobacteria / metabolism*
Proteome
Proteomics
Chemical
Reg. No./Substance:
0/Archaeal Proteins; 0/Ions; 0/Proteome; 660YQ98I10/Potassium Chloride; RWP5GA015D/Potassium
Comments/Corrections

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