Thermodynamic cooperativity of cosubstrate binding and cation selectivity of Salmonella typhimurium MelB.

ABSTRACT: The Na+-coupled melibiose symporter MelB, which can also be coupled to H+ or Li+ transport, is a prototype for the glycoside-pentoside-hexuronide:cation symporter family. Although the 3-D x-ray crystal structure of Salmonella typhimurium MelB (MelBSt) has been determined, the symport mechanisms for the obligatory coupled transport are not well understood. Here, we apply isothermal titration calorimetry to determine the energetics of Na+ and melibiose binding to MelBSt, as well as protonation of this transporter. Studies of the thermodynamic cycle for the formation of the Na+-MelBSt-melibiose ternary complex at pH 7.45 reveal that the binding of Na+ and melibiose is cooperative. The binding affinity for one substrate (Na+ or melibiose) is increased by the presence of the other by about eigh

SUBMITTER: Hariharan P 

PROVIDER: S-EPMC5677108 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature