MEKA/Phosducin Attenuates Hydrophobicity of Transducin βγ Subunits without Binding to Farnesyl Moiety

Abstract

Hydrophobic modifications of transducin (T)γ,such as farnesyl-and carboxyl-methylation, are essential for the association of Tβγ with the photoreceptor disc membrane, and MEKA/phosducin is known to inhibit the association. In this study, we examined the effect of MEKA on the hydrophobicity of Tβγ.MEKA could bind to Tβγ without farnesyl/carboxyl-methyl moieties as well as native Tβγ.In the Triton X-114 phase separation assay, Tβγ-MEKA complex was recovered in the aqueous phase, whereas Tβγ was recover in the detergent phase. N-terminal portion of MEKA which includes Tβγ-binding domain was not sufficient to reduce the hydrophobicity of Tβγ or to dissociate Tβγ from the membrane. The data suggest that MEKA attenuates the hydrophobicity of Tβγ to result in the dissociation of Tβγ from the membrane without directly binding to farnesyl/carboxyl-methyl moieties.