Alteration of Sugar-Induced Conformational Changes of the Melibiose Permease by Mutating Arg(141) in Loop 4-5

作者：Leon Xavier^*; Leblanc Gerard; Padros Esteve

来源：Biophysical Journal, 2009, 96(12): 4877-4886.

DOI：10.1016/j.bpj.2009.03.025

The melibiose permease (MelB) from Escherichia coli couples the uptake of melibiose to that of Na , Li , or H . In this work, we applied attenuated total reflection Fourier transform infrared (ATR-FTIR) difference spectroscopy to obtain information about the structural changes involved in substrate interaction with the R141 C mutant and with the wild-type MelB reacted with N-ethylmaleimide (NEM). These modified permeases have the ability to bind the substrates but fail to transport them. It is shown that the sugar-induced ATR-FTIR difference spectra of the R141C mutant are different from those corresponding to the Cys-less permease from which it is derived. There are alterations of peaks assigned to turns and beta-structures located most likely in loop 4-5. In addition, and quite notably, a peak at 1659 cm(-1), assigned to changes at the level of one a-helix subpopulation, disappears in the melibiose-induced difference spectrum in the presence of Na , suggesting a reduction of the conformational change capacity of the mutated MelB. These helices may involve structural components that couple the cation- and sugar-binding sites. On the other hand, MelB-NEM difference spectra are proportionally less disrupted than the R141C ones. Hence, the transport cycle of these two permeases, modified at two different loops, is most likely impaired at a different stage. It is proposed that the R141 C mutant leads to the generation of a partially defective ternary complex that is unable to catalyze the subsequent conformational change necessary for substrate translocation.

• 出版日期2009-6-17
• 单位中国地震局