MANNOSE TRANSPORTER OF ESCHERICHIA-COLI - BACKBONE ASSIGNMENTS AND SECONDARY STRUCTURE OF THE IIA DOMAIN OF THE IIAB(MAN) SUBUNIT

The mannose transporter of Escherichia coil consists of two transmembr ane and one peripheral protein subunit. The complex acts by a mechanis m which couples translocation of the substrate with substrate phosphor ylation. The peripheral IIAB(Man) is a homodimer. The IIAB(Man) monome r itself contains two domains which are linked by an Ala-Pro-rich hing e and which are both transiently phosphorylated at histidyl residues. The IIA and IIB domains can be separated by limited proteolysis. The I IA domain has a dimer molecular mass of 2 x 14 kDa. Almost complete H- 1,C-13, and N-15 NMR assignments of the backbone resonances of IIA(Man ) have been achieved using 3D and 4D double- and triple-resonance tech niques. Secondary structure elements were derived from NOE data. The I IA domain consists of a central beta-sheet of four parallel and one an tiparallel strand (strand order 5 4 3 1 2) with helices on both sides of the sheet. The active-site His-10 is located in a loop at the C-ter minus of beta-strand 1. This loop and the loop after strand 3 are at t he topological switch point of the sheet.