Thermodynamic study of the pH-dependent interaction of chromogranin A with an intraluminal loop peptide of the inositol 1,4,5-trisphosphate receptor.

Abstract

The secretory vesicles of adrenal chromaffin cells have previously been identified as a major inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store, and their Ca2+ store role has been attributed to the presence of chromogranin A, a high capacity, low affinity Ca2+ binding protein. Chromogranin A has since been shown to exist primarily in a dimeric state at pH 7.5 and primarily in a tetrameric state at the intravesicular pH of 5.5 and has also been shown to interact with the membrane proteins of secretory vesicles at pH 5.5, including a 260-kDa protein reactive to IP3 receptor antibody [Yoo, S. H. (1994) J. Biol. Chem. 269, 12001-12006]. In a recent study, chromogranin A was shown to interact with one of the intraluminal loop regions of the IP3 receptor at pH 5.5 but not at pH 7.5 [Yoo, S. H., & Lewis, M. S. (1994) FEBS Lett. 341, 28-32]. To gain further insight, we have studied the temperature dependence of the pH-dependent interaction of chromogranin A with the intraluminal peptide of the the IP3 receptor by analytical ultracentrifugation, using multiwavelength scan analysis, and found that four molecules of the intraluminal domain peptide of the IP3 receptor bound to each chromogranin A tetramer with delta Go values ranging from -23.6 to -27.6 kcal mol-1 in the absence and presence of 35 mN Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)