Interrelationships between protein phosphorylation and oligomerization in transport and chemotaxis via the Escherichia coli mannitol phosphotransferase system

The membrane-bound enzyme II of the bacterial carbohydrate phosphotransferase system (PTS) are multifunctional: they are required for the transport, phosphorylation and chemotactic sensing of their substrates. An oligomer (minimally a dimer) of at least one of these PTS permeases, the Escherichia coli mannitol permease, appears to be necessary for this protein to optimally carry out these functions. Much indirect evidence is consistent with this hypothesis, and recent experiments show that transport and phosphorylation of, and chemotaxis to, mannitol in E. coli involves an intersubunit phosphotransfer reaction, which can only occur in a protein oligomer. Membrane topological studies of the mannitol permease also argue in favour of an oligomeric structure in the membrane which may be necessary to form the hydrophilic channel through which mannitol must traverse the phospholipid bilayer. The possibility that the oligomerization state of the mannitol permease is a target for regulation of its activity in vivo is proposed, but has not yet been explored experimentally.