THE GLUCOSE-TRANSPORTER OF ESCHERICHIA-COLI ASSIGNMENT OF THE H-1, C-13 AND N-15 RESONANCES AND IDENTIFICATION OF THE SECONDARY STRUCTURE OF THE SOLUBLE IIB DOMAIN

The IICBGlc subunit of the Escherichia coli glucose transporter consis ts of two domains, the membrane-spanning IIC domain, and the hydrophil ic IIB domain which contains the phosphorylation site (Cys421). A func tional form of the IIB domain was over-expressed separately and isotop ically labelled with C-13 and N-15. A variety of N-15-edited and C-13, N-15 triple-resonance NMR experiments yielded a nearly complete assig nment of the H-1, C-13 and N-15 resonances. Based on the evaluation of conformationally sensitive parameters including NOE effects, scalar c ouplings and chemical shifts, the secondary structure of the IIB domai n is presented. The protein is comprised of four beta-strands forming an antiparallel beta-sheet, two larger alpha-helices at the N- and C-t ermini and a smaller helical structure of residues 52-58.