The mannose transporter of Escherichia coli. Structure and function of the IIABMan subunit.
The mannose transporter of the bacterial phosphotransferase system consists of two transmembrane subunits (IICMan and IIDMan) and a hydrophilic subunit (IIABMan). IIABMan has two flexibly linked domains containing one phosphorylation site each and occurs as a dimer. Substrate transport is coupled to phosphorylation. The phosphoryl group is transferred from a phosphoryl carrier protein to His10 on IIA, hence to His175 on IIB and finally to the substrate. IIABMan mutants were analyzed in vitro for complementation, negative dominance, cysteine cross-linking and reactivity.


CONCLUSIONS
(i) His10, Trp12, Lys48, and Ser72 form a functional unit (phosphorylation site 1); (ii) His86 on the IIA domain and His175 on the IIB domain of the same subunit form a functional unit (phosphorylation site 2); (iii) phosphoryl transfer can occur between His10 and His175 of the same as well as of different subunits and His86 is necessary for this transfer; (iv) the subunits in the dimer are interdependent; (v) The phosphorylation site mutant H175C is highly reactive toward thiol reagents and it forms extensive homo- and heterocross-links with other surface-exposed cysteines. The phosphorylation site mutant H10C is 1000-fold less reactive. The two residues might be in complementary locations, His10 buried in a concave, His175 exposed on a convex surface.
Stolz
B
B
Institute for Biochemistry, University of Bern, Switzerland.
Huber
M
M
Marković-Housley
Z
Z
Erni
B
B
D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003432:Cross-Linking Reagents; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism*; D005816:Genetic Complementation Test; D008358:Mannose / Q000378:metabolism*; D010084:Oxidation-Reduction; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D017354:Point Mutation; D011487:Protein Conformation
D001426:Bacterial Proteins; D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D010770:Phosphotransferases; D003545:Cysteine; D008358:Mannose