The mannose permease of Escherichia coli consists of three different proteins. Amino acid sequence and function in sugar transport, sugar phosphorylation, and penetration of phage lambda DNA

Abstract

The mannose permease of the bacterial phosphotransferase system mediates sugar transport across the cytoplasmic membrane concomitant with sugar phosphorylation. It also functions as a receptor for bacterial chemotaxis and is required for infection of the cell by bacteriophage lambda where it most likely functions as a pore for penetration of lambda DNA. The permease consists of three different subunits, IIIMan, II-PMan, and II-MMan, which are encoded in a single transcriptional unit ptsLPM. The complete amino acid sequence of the subunits is deduced from the nucleotide sequence. IIIMan (35 kDa) is a hydrophilic protein which is transiently phosphorylated and most likely contains the active site for sugar phosphorylation. II-PMan (28 kDa) is very hydrophobic; II-MMan (31 kDa) is moderately hydrophobic. Both are integral membrane proteins and most likely form the transmembrane channel. All three subunits are required for sugar transport and phosphorylation; II-PMan and II-MMan alone are sufficient for penetration of lambda DNA. Truncated forms of II-MMan and II-PMan are described that mediate lambda DNA penetration but have no apparent sugar transport activity. Residual sugar phosphorylation activity is found with the truncated form of II-PMan. No obvious homologies at the level of amino acid sequence could be detected with other bacterial transport proteins.