Skip to main content
NCBI home page
Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1982 Aug;79(15):4642–4644. doi: 10.1073/pnas.79.15.4642

Synexin facilitates fusion of specific phospholipid membranes at divalent cation concentrations found intracellularly.

K Hong, N Düzgüneş, R Ekerdt, D Papahadjopoulos
PMCID: PMC346731  PMID: 6214785

Abstract

The effect of synexin (an adrenal medullary protein) on the kinetics of Ca2+- and Mg2+-mediated membrane fusion was examined. Membrane fusion was studied by monitoring intermixing of the aqueous contents of phospholipid vesicles. Synexin facilitated Ca2+-mediated, but not Mg2+-mediated, fusion of phosphatidate/phosphatidylethanolamine (1:3) and phosphatidate/phosphatidylserine/phosphatidylethanolamine/cholesterol (1:2:3:2) vesicles. The threshold concentration of Ca2+ for fusion was decreased to approximately equal to 10 microM in the presence of synexin at 6 micrograms/ml and 1.5 mM Mg2+ in vesicle suspensions containing 50 microM lipid. This effect of synexin was drastically inhibited by including 25% phosphatidylcholine (mol/mol) in the vesicle membrane. It is proposed that the Ca2+-dependent lipid-specific enhancement of membrane fusion by synexin contributes to an increase in the sensitivity of specific intracellular membranes to Ca2+ with respect to fusion.

Full text

PDF
4642

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. BARTLETT G. R. Phosphorus assay in column chromatography. J Biol Chem. 1959 Mar;234(3):466–468. [PubMed] [Google Scholar]
  2. Creutz C. E., Pazoles C. J., Pollard H. B. Identification and purification of an adrenal medullary protein (synexin) that causes calcium-dependent aggregation of isolated chromaffin granules. J Biol Chem. 1978 Apr 25;253(8):2858–2866. [PubMed] [Google Scholar]
  3. Düzgünes N., Nir S., Wilschut J., Bentz J., Newton C., Portis A., Papahadjopoulos D. Calcium- and magnesium-induced fusion of mixed phosphatidylserine/phosphatidylcholine vesicles: effect of ion binding. J Membr Biol. 1981 Apr 15;59(2):115–125. doi: 10.1007/BF01875709. [DOI] [PubMed] [Google Scholar]
  4. Düzgüneş N., Wilschut J., Fraley R., Papahadjopoulos D. Studies on the mechanism of membrane fusion. Role of head-group composition in calcium- and magnesium-induced fusion of mixed phospholipid vesicles. Biochim Biophys Acta. 1981 Mar 20;642(1):182–195. doi: 10.1016/0005-2736(81)90148-6. [DOI] [PubMed] [Google Scholar]
  5. Ekerdt R., Dahl G., Gratzl M. Membrane fusion of secretory vesicles and liposomes. Two different types of fusion. Biochim Biophys Acta. 1981 Aug 6;646(1):10–22. doi: 10.1016/0005-2736(81)90265-0. [DOI] [PubMed] [Google Scholar]
  6. Fraley R., Wilschut J., Düzgüneş N., Smith C., Papahadjopoulos D. Studies on the mechanism of membrane fusion: role of phosphate in promoting calcium ion induced fusion of phospholipid vesicles. Biochemistry. 1980 Dec 23;19(26):6021–6029. doi: 10.1021/bi00567a012. [DOI] [PubMed] [Google Scholar]
  7. Gilkey J. C., Jaffe L. F., Ridgway E. B., Reynolds G. T. A free calcium wave traverses the activating egg of the medaka, Oryzias latipes. J Cell Biol. 1978 Feb;76(2):448–466. doi: 10.1083/jcb.76.2.448. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. HODGKIN A. L., KEYNES R. D. Movements of labelled calcium in squid giant axons. J Physiol. 1957 Sep 30;138(2):253–281. doi: 10.1113/jphysiol.1957.sp005850. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Hong K., Düzgüneş N., Papahadjopoulos D. Modulation of membrane fusion by calcium-binding proteins. Biophys J. 1982 Jan;37(1):297–305. doi: 10.1016/S0006-3495(82)84678-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Hong K., Düzgüneş N., Papahadjopoulos D. Role of synexin in membrane fusion. Enhancement of calcium-dependent fusion of phospholipid vesicles. J Biol Chem. 1981 Apr 25;256(8):3641–3644. [PubMed] [Google Scholar]
  11. Portis A., Newton C., Pangborn W., Papahadjopoulos D. Studies on the mechanism of membrane fusion: evidence for an intermembrane Ca2+-phospholipid complex, synergism with Mg2+, and inhibition by spectrin. Biochemistry. 1979 Mar 6;18(5):780–790. doi: 10.1021/bi00572a007. [DOI] [PubMed] [Google Scholar]
  12. SINGLETON W. S., GRAY M. S., BROWN M. L., WHITE J. L. CHROMATOGRAPHICALLY HOMOGENEOUS LECITHIN FROM EGG PHOSPHOLIPIDS. J Am Oil Chem Soc. 1965 Jan;42:53–56. doi: 10.1007/BF02558256. [DOI] [PubMed] [Google Scholar]
  13. Steinhardt R., Zucker R., Schatten G. Intracellular calcium release at fertilization in the sea urchin egg. Dev Biol. 1977 Jul 1;58(1):185–196. doi: 10.1016/0012-1606(77)90084-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Sundler R., Düzgüneş N., Papahadjopoulos D. Control of membrane fusion by phospholipid head groups. II. The role of phosphatidylethanolamine in mixtures with phosphatidate and phosphatidylinositol. Biochim Biophys Acta. 1981 Dec 21;649(3):751–758. doi: 10.1016/0005-2736(81)90180-2. [DOI] [PubMed] [Google Scholar]
  15. Sundler R., Papahadjopoulos D. Control of membrane fusion by phospholipid head groups. I. Phosphatidate/phosphatidylinositol specificity. Biochim Biophys Acta. 1981 Dec 21;649(3):743–750. doi: 10.1016/0005-2736(81)90179-6. [DOI] [PubMed] [Google Scholar]
  16. Szoka F., Jr, Papahadjopoulos D. Procedure for preparation of liposomes with large internal aqueous space and high capture by reverse-phase evaporation. Proc Natl Acad Sci U S A. 1978 Sep;75(9):4194–4198. doi: 10.1073/pnas.75.9.4194. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Wilschut J., Düzgüneş N., Fraley R., Papahadjopoulos D. Studies on the mechanism of membrane fusion: kinetics of calcium ion induced fusion of phosphatidylserine vesicles followed by a new assay for mixing of aqueous vesicle contents. Biochemistry. 1980 Dec 23;19(26):6011–6021. doi: 10.1021/bi00567a011. [DOI] [PubMed] [Google Scholar]
  18. Wilschut J., Düzgüneş N., Papahadjopoulos D. Calcium/magnesium specificity in membrane fusion: kinetics of aggregation and fusion of phosphatidylserine vesicles and the role of bilayer curvature. Biochemistry. 1981 May 26;20(11):3126–3133. doi: 10.1021/bi00514a022. [DOI] [PubMed] [Google Scholar]
  19. Wilschut J., Papahadjopoulos D. Ca2+-induced fusion of phospholipid vesicles monitored by mixing of aqueous contents. Nature. 1979 Oct 25;281(5733):690–692. doi: 10.1038/281690a0. [DOI] [PubMed] [Google Scholar]

Articles from Proceedings of the National Academy of Sciences of the United States of America are provided here courtesy of National Academy of Sciences

RESOURCES