RECOVERIN ALTERS ITS SURFACE-PROPERTIES DEPENDING ON BOTH CALCIUM-BINDING AND N-TERMINAL MYRISTOYLATION

The solution structure and calcium-dependent structural changes of rec overin, a 23 kDa calcium binding protein of vertebrate photoreceptors, have been studied by small-angle X-ray scattering and CD, as well is the effect of N-terminal myristoylation. The CD spectrum is not affect ed by N-terminal myristoylation, but strongly affected by Ca2+, indica ting that N-terminal myristoylation alone does not cause a conformatio nal change. The major conformational change in recoverin induced by Ca 2+ is characterized as a decrease in the a-helical content of the prot ein and an increase in global size upon removal of Ca2+. In the presen ce of Ca2+, unmyristoylated recoverin is monomeric and globular in sol ution, while N-terminal myristoylation brings about aggregation. In th e absence of Ca2+, unmyristoylated recoverin tends to aggregate, while myristoylated recoverin becomes monomeric and globular. These observa tions indicate that recoverin changes its surface properties depending on both calcium binding and N-terminal myristoylation. Melittin inter acts non-specifically only with the myristoylated recoverin in the abs ence of Ca2+. This may be indicative of the properties of the interact ion between recoverin and its normal physiological target enzyme.