The glucose transporter of Escherichia coli Assignment of the ¹H, ¹³C and ¹⁵N resonances and identification of the secondary structure of the soluble IIB domain

The IICB^Glc subunit of the Escherichia coli glucose transporter consists of two domains, the membrane‐spanning IIC domain, and the hydrophilic IIB domain which contains the phosphorylation site (Cys421). A functional form of the IIB domain was over‐expressed separately and isotopically labelled with ¹³C and ¹⁵N. A variety of ¹⁵N‐edited and ¹³C, ¹⁵N triple‐resonance NMR experiments yielded a nearly complete assignment of the ¹H, ¹³C and ¹⁵N resonances. Based on the evaluation of conformationally sensitive parameters including NOE effects, scalar couplings and chemical shifts, the secondary structure of the IIB domain is presented. The protein is comprised of four β‐strands forming an antiparallel β‐sheet, two larger α‐helices at the N‐ and C‐termini and a smaller helical structure of residues 52–58.