CYSTEINE PHOSPHORYLATION OF THE GLUCOSE TRANSPORTER OF ESCHERICHIA-COLI

The glucose transporter (IIBC(Glc)/IIA(Glc) complex) of the bacterial phosphotransferase system couples vectorial translocation to phosphory lation of the transported sugar. The IIA(Glc) subunit transfers the ph osphoryl group from the phosphoryl carrier protein P-HPr to the IIBC(G lc) subunit. IIBC(Glc) translocates and phosphorylates glucose. The si te of IIBC(Glc) phosphorylation is cysteine 421 as shown by mass spect rometric and biochemical analyses of phosphorylated peptides. Site-dir ected mutagenesis of Cys421 (C421S) afforded a stable but completely i nactive protein (Nuoffer, C., Zanolari, B., and Erni, B. (1988) J. Bio l. Chem. 263, 6647-6655). Cys421 is located in the C-terminal cytoplas mic domain of the IIBC(Glc) subunit in a sequence context (LDACITRL) w hich is well conserved in other transporters of the bacterial phosphot ransferase system. Phosphocysteine has been shown previously to be the catalytic intermediate of the mannitol transporter (Pas, H. H., Meyer , G. H., Kruizinga, W. H., Tamminga, K. S., van Weeghel, R. P., and Ro billard, G. T. (1991) J. Biol. Chem. 266, 6690-6692).