TY - JOUR
T1 - An essential role for UshA in processing of extracellular flavin electron shuttles by Shewanella oneidensis
AU - Covington, Elizabeth D.
AU - Gelbmann, Christopher B.
AU - Kotloski, Nicholas J.
AU - Gralnick, Jeffrey A.
PY - 2010/10/1
Y1 - 2010/10/1
N2 - The facultative anaerobe Shewanella oneidensis can reduce a number of insoluble extracellular metals. Direct adsorption of cells to the metal surface is not necessary, and it has been shown that S. oneidensis releases low concentrations flavins, including riboflavin and flavin mononucleotide (FMN), into the surrounding medium to act as extracellular electron shuttles. However, the mechanism of flavin release by Shewanella remains unknown. We have conducted a transposon mutagenesis screen to identify mutants deficient in extracellular flavin accumulation. Mutations in ushA, encoding a predicted 5′-nucleotidase, resulted in accumulation of flavin adenine dinucleotide (FAD) in culture supernatants, with a corresponding decrease in FMN and riboflavin. Cellular extracts of S. oneidensis convert FAD to FMN, whereas extracts of ushA mutants do not, and fractionation experiments show that UshA activity is periplasmic. We hypothesize that S. oneidensis secretes FAD into the periplasmic space, where it is hydrolysed by UshA to FMN and adenosine monophosphate (AMP). FMN diffuses through outer membrane porins where it accelerates extracellular electron transfer, and AMP is dephosphorylated by UshA and reassimilated by the cell. We predict that transport of FAD into the periplasm also satisfies the cofactor requirement of the unusual periplasmic fumarate reductase found in Shewanella.
AB - The facultative anaerobe Shewanella oneidensis can reduce a number of insoluble extracellular metals. Direct adsorption of cells to the metal surface is not necessary, and it has been shown that S. oneidensis releases low concentrations flavins, including riboflavin and flavin mononucleotide (FMN), into the surrounding medium to act as extracellular electron shuttles. However, the mechanism of flavin release by Shewanella remains unknown. We have conducted a transposon mutagenesis screen to identify mutants deficient in extracellular flavin accumulation. Mutations in ushA, encoding a predicted 5′-nucleotidase, resulted in accumulation of flavin adenine dinucleotide (FAD) in culture supernatants, with a corresponding decrease in FMN and riboflavin. Cellular extracts of S. oneidensis convert FAD to FMN, whereas extracts of ushA mutants do not, and fractionation experiments show that UshA activity is periplasmic. We hypothesize that S. oneidensis secretes FAD into the periplasmic space, where it is hydrolysed by UshA to FMN and adenosine monophosphate (AMP). FMN diffuses through outer membrane porins where it accelerates extracellular electron transfer, and AMP is dephosphorylated by UshA and reassimilated by the cell. We predict that transport of FAD into the periplasm also satisfies the cofactor requirement of the unusual periplasmic fumarate reductase found in Shewanella.
UR - http://www.scopus.com/inward/record.url?scp=78649371078&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=78649371078&partnerID=8YFLogxK
U2 - 10.1111/j.1365-2958.2010.07353.x
DO - 10.1111/j.1365-2958.2010.07353.x
M3 - Article
C2 - 20807196
AN - SCOPUS:78649371078
SN - 0950-382X
VL - 78
SP - 519
EP - 532
JO - Molecular Microbiology
JF - Molecular Microbiology
IS - 2
ER -