Interaction of chromogranin B and the near N-temninal region of chromogranin B with an intraluminal loop peptide of the inositol 1,4,5-trisphosphate receptor

Given the interaction of the inositol 1,4,5-trisphosphate receptor (IP3R) with chromogranins A (CGA) and B (CGB), two major Ca2+ storage proteins of secretory granules that have been shown to be IP3-sensitive intracellular Ca2+ store of neuroendocrine cells, we have investigated the potential interaction of the intraluminal loop regions of the IP3R with both intact CGB and the conserved near N-terminal region of CGB. The interaction studies carried out with CGB and glutathione S-transferase fusion proteins of intraluminal loop regions of bovine type 1 IP3R showed that CGB interacts with intraluminal loop 3-2 (the second loop formed between transmembrane regions 5 and 6) of the IP3R at both pH 5.5 and 7.5. Analytical ultracentrifugation studies also indicated-that CGB interacts with the same intraluminal loop region of the IP3R and the interaction was much stronger than that between CGA and the loop. Moreover, the conserved near N-terminal region of CGB also interacted with the intraluminal loop region of the IP3R. The CGB interaction with the IP3R intraluminal loop peptide at pH 7.5 showed a Delta G(0) value of -8.1 kcal/ mol at 37 degrees C for a 1:1 stoichiometry, indicating a K-d of similar to 1.9 mu M. These results give insight into the molecular organization of the IP3-sensitive Ca2+ store.