Analysis of the Tβγ-binding domain of MEKA/phosducin

Abstract

MEKA/phosducin, a 33 kDa phosphoprotein in the photoreceptor cell, associates with transducin βγ(Tβγ) with its N-terminal domain (N-terminal 105 amino acids of MEKA), and translocates Tβγ from the photoreceptor disc membrane to the soluble fraction. The present study further localized the Tβγ-binding domain to aa 17–105 of MEKA, and showed that the activity of MEKA to translocate Tβγ depends on the domain. A series of deletion mutant MEKA proteins were prepared to investigate the domain of MEKA which binds to and translocates Tβγ. Both binding and translocation activities were not impaired by the deletion of the N-terminal 16 amino acids of MEKA, but completely abolished by further deletion to 42Val. Although anti-MEKA serum inhibited the Tβγ-MEKA association, the antiserum absorbed with a recombinant peptide corresponding to aa 17–105 of MEKA did not, confirming that aa 17–105 of MEKA directly interacts with Tβγ.