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Evidence for two distinct conformations of the Escherichia coli mannitol permease that are important for its transport and phosphorylation functions
Author(s) -
Khandekar Sanjay S.,
Jacobson Gary R.
Publication year - 1989
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240390212
Subject(s) - permease , pep group translocation , mannitol , dimer , phosphorylation , chemistry , biochemistry , phosphotransferase , phosphoenolpyruvate carboxykinase , monomer , escherichia coli , phosphate , enzyme , gene , organic chemistry , polymer
Column chromatography of the Escherichia coli mannitol permease (mannitolspecific enzyme II of the phosphotransferase system) in the presence of deoxycholate has revealed that the active permease can exist in at least two association states with apparent molecular weights consistent with a monomer and a dimer. The monomeric conformation is favored by the presence of mannitol and by the phosphoenolpyruvate (PEP)‐dependent phosphorylation of the protein. The dimer is stabilized by inorganic phosphate (Pi), which also stimulates phospho‐exchange between mannitol and mannitol 1‐phosphate (a partial reaction in the overall PEP‐dependent phosphorylation of mannitol). Kinetic analysis of the phospho‐exchange reaction revealed that Pi stimulates phospho‐exchange by increasing the V max of the reaction. A kinetic model for mannitol permease function is presented involving both conformations of the permease. The monomer (or a less‐stable conformation of the dimer) is hypothesized to be involved in the initial mannitol‐binding and PEP‐dependent phosphorylation steps, while the stably associated dimer is suggested to participate in later steps involving direct phosphotransfer between the permease, mannitol and mannitol 1‐phosphate.