Conformational changes of the histidine ATP-binding cassette transporter studied by double electron-electron resonance spectroscopy.

Abstract The conformational dynamics of the histidine ABC transporter HisQMP 2 from Salmonella enterica serovar Typhimurium, reconstituted into liposomes, is studied by site-directed spin labeling and double electron–electron resonance spectroscopy in the absence of nucleotides, in the ATP-bound, and in the post-hydrolysis state. The results show that the inter-dimer distances as measured between the Q-loops of HisP 2 in the intact transporter resemble those determined for the maltose transporter in all three states of the hydrolysis cycle. Only in the presence of liganded HisJ the closed conformation of the nucleotide binding sites is achieved revealing the transmembrane communication of the presence of substrate. Two conformational states can be distinguished for the periplasmic moiety of HisQMP 2 as detected by differences in distributions of interspin distances between positions 86 and 96 or 104 and 197. The observed conformational changes are correlated to proposed open, semi-open and closed conformations of the nucleotide binding domains HisP 2 . Our results are in line with a rearrangement of transmembrane helices 4 and 4′ of HisQM during the closed to the semi-open transition of HisP 2 driven by the reorientation of the coupled helices 3a and 3b to occur upon hydrolysis.