The Walker B sequence in ABC transporters is responsible for:
Walker B motif in ABC nucleotide-binding domains follows consensus hhhhDE where h denotes hydrophobic residue. This segment forms beta-strand adjacent to Walker A P-loop. The aspartate carboxylate coordinates Mg2+ ion essential for ATP binding and neutralizing negative charge of phosphate chain, while downstream glutamate acts as catalytic base activating water for nucleophilic attack on gamma phosphate during hydrolysis. Structural studies of MalK, Sav1866 and P-glycoprotein show glutamate positioned near gamma phosphate; mutation to glutamine yields hydrolysis-deficient protein that binds AT
Ref: Oldham & Chen, J Mol Biol 2008, ABC NBD catalytic mechanism; Jones & George, 2004, Walker B role.
