J. Biol. Chem., Vol. 262, Issue 16, 7850-7858, Jun, 1987
Synexin-like proteins from human polymorphonuclear leukocytes. Identification and characterization of granule-aggregating and membrane- fusing activities
P Meers, JD Ernst, N Duzgunes, KL Hong, J Fedor, IM Goldstein and D Papahadjopoulos
We have used Ca2+-dependent binding to a phospholipid vesicle affinity
column to isolate a mixture of three synexin-like proteins from the cytosol
of human polymorphonuclear leukocytes (PMN), with relative molecular
weights of approximately 67,000, 47,000, and 28,000. Rabbit antibodies
raised against bovine liver synexin recognized the 47,000 molecular weight
PMN protein. These PMN proteins, like bovine liver synexin, promoted
aggregation of isolated PMN specific granules in the presence of Ca2+ and
increased the overall rate of Ca2+-induced fusion of liposomes composed of
phosphatidate (PA)/phosphatidylethanolamine (PE) (1:3) and
phosphatidylserine/PE (1:3), but decreased the rate of spermine-induced
fusion of PA/PE (1:3) liposomes. Using fluorescent lipid probes, rapid
fusion of PA/PE liposomes with PMN specific granules (50% maximum signal
within a few minutes) was observed when 1 mM Ca2+ was added in the presence
of both synexin and free arachidonic acid. Dilution of the aqueous contents
of liposomes was also observed under the same conditions. The rate of
fusion increased monotonically with Ca2+ and arachidonic acid
concentrations, but synexin exhibited an optimum concentration. Lack of any
one of the components precluded rapid fusion. These results suggest that
PMN contain a protein similar to, or identical with, synexin that may be
involved in calcium- dependent fusion of intracellular membranes.
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