Presence of secretogranin II and high-capacity, low-affinity Ca2+ storage role in nucleoplasmic Ca2+ store vesicles.
Chromogranins and secretogranins have traditionally been known as marker proteins of secretory granules that contain the highest concentrations of cellular calcium, reaching approximately 40 mM. In addition, chromogranin B was also shown to exist in the nucleus, localizing in the putative inositol 1,4,5-trisphosphate (IP3)-sensitive nucleoplasmic Ca2+ store vesicles. Chromogranins A (CGA) and B (CGB) are high-capacity, low-affinity Ca2+ binding proteins, binding 30-90 mol of Ca2+/mol with dissociation constants (Kd) of 1.5-4 mM. Yet the Ca2+-binding property of secretogranins has not been studied. Here, we show the localization of secretogranin II (SgII) in the nucleus, more specifically, in the IP3-sensitive nucleoplasmic Ca2+ store vesicles along with CGB and the IP3 receptors. We have also determined the Ca2+-binding property of SgII and found that SgII binds 61 mol of Ca2+/mol (910 nmol Ca2+/mg) with a Kd of 3.0 mM at the intragranular pH 5.5 and 30 mol of Ca2+/mol (440 nmol Ca2+/mg) with a Kd of 2.2 mM at a near-physiological pH 7.5. Chromogranin B also bound 50 mol of Ca2+/mol (670 nmol Ca2+/mg) with a Kd of 3.1 mM at pH 7.5. Given the high-capacity, low-affinity Ca2+-binding property of SgII and its presence in the IP3-sensitive nucleoplasmic Ca2+ store vesicles, these results suggest that SgII may function in the storage and control of Ca2+ in the nucleus through its interaction with CGB in the nucleoplasmic vesicles.
Yoo
Seung Hyun
SH
Department of Biochemistry, Inha University College of Medicine, Jung Gu, Incheon 400-712, Korea. shyoo@inha.ac.kr
Chu
Sei Yoon
SY
Kim
Ki Deok
KD
Huh
Yang Hoon
YH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D002837:Chromaffin Granules / Q000378:metabolism / Q000648:ultrastructure; D053378:Chromogranin B / Q000378:metabolism / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D047468:Immunoprecipitation; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D011485:Protein Binding; D053381:Secretogranin II / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
D053378:Chromogranin B; D053496:Inositol 1,4,5-Trisphosphate Receptors; D053381:Secretogranin II; D002118:Calcium