Interactions of cyclic nucleotide-gated channel subunits and protein tyrosine kinase probed with genistein

The cGMP sensitivity of cyclic nucleotide-gated (CNG) channels can be modul ated by changes in phosphorylation catalyzed by protein tyrosine kinases (P TKs) and protein tyrosine phosphatases. Previously, we used genistein, a PT K inhibitor, to probe the interaction between PTKs and homomeric channels c omprised of alpha subunits (RET alpha) of rod photoreceptor CNG channels ex pressed in Xenopus oocytes. We showed that in addition to inhibiting phosph orylation, genistein triggers a noncatalytic interaction between PTKs and h omomeric RET alpha channels that allosterically inhibits channel gating. He re, we show that native CNG channels from rods, cones, and olfactory recept or neurons also exhibit noncatalytic inhibition induced by genistein, sugge sting that in each of these sensory cells, CNG channels are part of a regul atory complex that contains PTKs. Native CNG channels are heteromers, conta ining beta as well as alpha subunits. To determine the contributions of alp ha and beta subunits to genistein inhibition, we compared the effect of gen istein on native, homomeric (RET alpha and OLF alpha), and heteromeric (RET alpha+beta, OLF alpha+beta, and OLF alpha+RET beta) CNG channels. We found that genistein only inhibits channels that contain either the RET alpha or the OLF beta subunits. This finding, along with other observations about t he maximal effect of genistein and the Hill coefficient of genistein inhibi tion, suggests that the RET alpha and OLF beta subunits contain binding sit es for the PTK, whereas RET beta and OLF alpha subunits do not.