Identification of a new porin, RafY, encoded by raffinose plasmid pRSD2 of Escherichia coli

Autor(en): Ulmke, C
Lengeler, JW
Schmid, K
Stichwörter: DIFFUSION CHANNELS; GENES; LAMBDA-RECEPTOR; MALTOPORIN CHANNELS; MALTOSE-BINDING PROTEIN; MEDIATED SUCROSE METABOLISM; Microbiology; MUTAGENESIS; NUCLEOTIDE-SEQUENCES; SCRY; TRANSPORT
Erscheinungsdatum: 1997
Herausgeber: AMER SOC MICROBIOLOGY
Journal: JOURNAL OF BACTERIOLOGY
Volumen: 179
Ausgabe: 18
Startseite: 5783
Seitenende: 5788
Zusammenfassung: 
The conjugative plasmid pRSD2 carries a raf operon that encodes a peripheral raffinose metabolic pathway in enterobacteria. In addition to the previously known raf genes, we identified another gene, rafY, which in Escherichia coli codes for an outer membrane protein (molecular mass, 53 kDa) similar in function to the known glycoporins LamB (maltoporin) and ScrY (sucrose porin), Sequence comparisons with LamB and ScrY revealed no significant similarities; however, both lamB and scrY mutants are functionally complemented by RafY, Expressed from the tac promoter, RafY significantly increases the uptake rates for maltose, sucrose, and raffinose at low substrate concentrations; in particular it shifts the apparent K-m for raffinose transport from 2 mM to 130 mu M. Moreover, RafY permits diffusion of the tetrasaccharide stachyose and of maltodextrins up to maltoheptaose through the outer membrane of E. coli, A comparison of all three glycoporins in regard to their substrate selectivity revealed that both ScrY and RafY have a broad substrate range which includes alpha-galactosides while LamB seems to be restricted to malto-oligosaccharides. It supports growth only on maltodextrins but not, like the others, on raffinose and stachyose.
ISSN: 00219193
DOI: 10.1128/jb.179.18.5783-5788.1997

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