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

Abstract

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 ΔG0 value of -8.1 kcal/mol at 37 °C for a 1:1 stoichiometry, indicating a K(d) of ~1.9 μM. These results give insight into the molecular organization of the IP3-sensitive Ca2+ store.