Document Detail

Streptomyces lividans potassium channel contains poly-(R)-3-hydroxybutyrate and inorganic polyphosphate.
MedLine Citation:
PMID:  10569953     Owner:  NLM     Status:  MEDLINE    
The Streptomyces lividans KcsA potassium channel, a homotetramer of 17.6 kDa subunits, was found to contain two nonproteinaceous polymers, namely, poly-(R)-3-hydroxybutyrate (PHB) and inorganic polyphosphate (polyP). PHB and polyP are ubiquitous cellular constituents with a demonstrated capacity for cation selection and transport. PHB was detected in both tetramer and monomer species of KcsA by reaction to anti-PHB IgG on Western blots, and estimated as 28 monomer units of PHB per KcsA tetramer by a chemical assay in which PHB is converted to its unique degradation product, crotonic acid. PolyP was detected in KcsA tetramers, but not in monomers, by metachromatic reaction to o-toluidine blue stain on SDS-PAGE gels. A band of free polyP was also visible, suggesting that polyP is released when tetramers dissociate. The exopolyphosphatase of Saccharomyces cerevisiae degraded the free polyP, but tetramer-associated polyP was not affected, indicating it was inaccessible to the enzyme. PolyP in KcsA was estimated as 15 monomer units per tetramer by an enzymatic assay in which polyphosphate kinase is used to transfer phosphates from polyP to [(14)C]ADP, yielding [(14)C]ATP. The experimentally determined isoelectric point of KcsA tetramer was 6.5-7.5, substantially more acidic than the theoretical pI of 10.3, and consistent with the inclusion of a polyanion. The results suggest that PHB is covalently bound to KcsA subunits while polyP is held within tetramers by ionic forces. It is posited that KcsA protein creates an environment in which PHB/polyP is selective for K(+). The basic amino acids attenuate the negative charge density of polyP, thereby transforming the cation binding preference from multivalent to monovalent, and discrimination between K(+) and Na(+) is accomplished by adjusting the ligand geometry in cation binding cavities formed by PHB and polyP.
R N Reusch
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  38     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1999 Nov 
Date Detail:
Created Date:  1999-12-16     Completed Date:  1999-12-16     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  15666-72     Citation Subset:  IM    
Department of Microbiology, Michigan State University, East Lansing 48824, USA.
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MeSH Terms
Bacterial Proteins / chemistry*
Biopolymers / chemistry
Blotting, Western
Electrophoresis, Polyacrylamide Gel
Hydroxybutyrates / isolation & purification*
Isoelectric Point
Polyesters / isolation & purification*
Polyphosphates / isolation & purification*
Potassium Channels / chemistry*
Streptomyces / chemistry*
Grant Support
Reg. No./Substance:
0/Bacterial Proteins; 0/Biopolymers; 0/Hydroxybutyrates; 0/Polyesters; 0/Polyphosphates; 0/Potassium Channels; 0/prokaryotic potassium channel; 26063-00-3/poly-beta-hydroxybutyrate

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