CFTR, the anion channel mutated in cystic fibrosis patients, is a model ABC protein
whose ATP-driven conformational cycle is observable at single-molecule level in patch-clamp
recordings. Bursts of CFTR pore openings are coupled to tight dimerization of its
two nucleotide-binding domains (NBDs) and in wild-type (WT) channels are mostly terminated
by ATP hydrolysis. The slow rate of non-hydrolytic closure - which determines how
tightly bursts and ATP hydrolysis are coupled - is unknown, as burst durations of
catalytic site mutants span a range of ~200-fold. Here, we show that Walker A mutation
K1250A, Walker B mutation D1370N, and catalytic glutamate mutations E1371S and E1371Q
all completely disrupt ATP hydrolysis. True non-hydrolytic closing rate of WT CFTR
approximates that of K1250A and E1371S. That rate is slowed ~15-fold in E1371Q by
a non-native inter-NBD H-bond, and accelerated ~15-fold in D1370N. These findings
uncover unique features of the NBD interface in human CFTR.
