To clarify the potentiation mechanism of genistein, we propose
point mutations at the following residues to identify the binding
site(s) of genistein: F490, F494 and W496 on NBD1, and P1290,
F1294, F1296, and H1348 on NBD2 (seeFig. 6). Converting one of
these residues to glycine or alanine is expected to remove the
corresponding ring–ring stacking interaction between genistein
andCFTR at sites 2 or 3 and therefore reduce binding tightness. Our
preliminary study with F494G-CFTR using whole-cell electro-physiological recording showed that indeed the apparent affinity
of genistein was lowered to 25.3mM, compared to 4.4mM for
wild-type CFTR (M. Li and T.-C. Hwang, unpublished data). Future
whole-cell dose–response measurements and further single-channel studies on these mutated CFTR channels together with
control experiments would clarify whether genistein binds to
either or both sites 2 and 3. The findings would provide valuable
information for rational drug design targeting at CFTR for the
treatment of cystic fibrosis