L. Lichtenbergova et al., MEMBRANE PENETRATION OF CYTOSOLIC PHOSPHOLIPASE A(2) IS NECESSARY FORITS INTERFACIAL CATALYSIS AND ARACHIDONATE SPECIFICITY, Biochemistry (Easton), 37(40), 1998, pp. 14128-14136
To determine the mechanism of calcium-dependent membrane binding of cy
tosolic phospholipase A(2) (cPLA(2)), we measured the interactions of
cPLA(2) with phospholipid monolayers and polymerizable mixed liposomes
containing various phospholipids. In the presence of calcium, cPLA(2)
showed much higher penetrating power than secretory human pancreatic
PLA(2) toward anionic and electrically neutral phospholipid monolayers
. cPLA(2) also showed ca. 30-fold higher binding affinity for nonpolym
erized lipoyloxy)dodecanoyl]-sn-glycero-1-phosphoglycerol (D-BLPG) lip
osomes than for polymerized ones where the membrane penetration of pro
tein is significantly restricted. Consistent with this difference in m
embrane binding affinity, cPLA(2) showed 20-fold higher activity towar
d fluorogenic substrates, decyl)-2-arachidonoyl-sn-glycero-3-phosphoch
oline, inserted in nonpolymerized D-BLPG liposomes than the same subst
rate in polymerized D-BLPG liposomes. Furthermore, cPLA(2) showed much
higher sn-2 acyl group specificity (arachidonate specificity) and hea
dgroup specificity in nonpolymerized D-BLPG liposomes than in polymeri
zed D-BLPG liposomes. Finally, diacylglycerols, such as 1,2-dioleoyl-s
n-glycerol, selectively enhanced the membrane penetration, hydrophobic
membrane binding, and interfacial enzyme activity of cPLA(2). Taken t
ogether, these results indicate the following: (1) calcium not only br
ings cPLA(2) to the membrane surface but also induces its membrane pen
etration. (2) This unique calcium-dependent membrane penetration of cP
LA(2) is necessary for its interfacial binding and substrate specifici
ty. (3) Diacylglycerols might work as a cellular activator of cPLA(2)
by enhancing its membrane penetration and hydrophobic membrane binding
.