FUNCTIONAL EXPRESSION AND CHARACTERIZATION OF FROG PHOTORECEPTOR-SPECIFIC CALCIUM-BINDING PROTEINS

S-modulin (sensitivity-modulating protein) is a photoreceptor-specific calcium-binding protein which plays an important role in the light ad aptation process by controlling rhodopsin phosphorylation in rods. S-m odulin and its cone homologue, s26, were expressed at high level (more than 30% of total protein) in Escherichia coli and then purified. The y both inhibited rhodopsin phosphorylation in a calcium dependent mann er. Myristoylated recombinants of S-modulin and s26 showed calcium-dep endent changes in tryptophan emission spectra with half-maxima at abou t 0.7 mu M free calcium concentration. However, the spectral changes a re distinctive from each other, suggesting that there is some differen ce in the structural change between S-modulin and s26. (C) 1997 Academ ic Press.