Isolation and characterization of calcium(2+) ion-dependent modulator protein from the marine invertebrate Renilla reniformis

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Abstract
An acidic, low MW (18,400-19,100) protein capable of activating porcine brain phosphodiesterase in the presence of Ca was purified 2700-fold from the anthozoan coelenterate, R. reniformis. The protein has physicial, spectral and chemical properties similar to those of modulator proteins isolated from mammalian species. Amino acid composition studies reveal no significant differences between the Renilla and mammalian modulator proteins. The protein had 1 mol of .epsilon.-N-trimethyllysine/mol, no tryptophan or cysteine and high levels of glutamic and aspartic acid residues. The protein from Renilla complexes with troponin I and T subunits in the presence of Ca and quantitatively replaces porcine brain modulator in the Ca-dependent activation of porcine brain phosphodiesterase. The protein has a high affinity for Ca as judged by the low levels of free Ca required for modulator-dependent activation of phosphodiesterase. The similarities in physical and chemical properties, high affinity for Ca and identical Ca-dependent activities of this protein from Renilla (as compared with modulator protein purified from mammalian systems) suggest that a high degree of structural conservation was retained in modulator proteins isolated from these diverse evolutionary forms.

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