Analysis of the cyclic nucleotide binding domain of the HERG potassium channel and interactions with KCNE2

Mutations in the cyclic nucleotide binding domain (CNBD) of the human ether -a-go-go-related gene (HERG) K+ channel are associated with LQT2, a form of hereditary Long QT syndrome (LQTS), Elevation of cAMP can modulate HERG K channels both by direct binding and indirect regulation through protein ki nase A. To assess the physiological significance of cAMP binding to HERG, w e introduced mutations to disrupt the cyclic nucleotide binding domain. Eig ht mutants including two naturally occurring LQT2 mutants V822M and R823W w ere constructed. Relative cAMP binding capacity was reduced or absent in CN BD mutants. Mutant homotetramers carry little or no K+ current despite norm al protein abundance and surface expression. Co-expression of mutant and wi ld-type HERG; resulted in currents with altered voltage dependence but with out dominant current suppression. The data from co-expression of V822M and wild-type HERG best fit a model where one normal subunit within a tetramer allows nearly normal current expression, The presence of KCNE2, an accessor y protein that associates with HERG, however, conferred a partially dominan t current suppression by CNBD mutants. Thus KCNE2 plays a pivotal role in d etermining the phenotypic severity of some forms of LQT2, which suggests th at the CNBD of HERG may be involved in its interaction with KCNE2.