PLASMA-MEMBRANE LOCALIZATION OF G-ALPHA(Z) REQUIRES 2 SIGNALS

Citation
J. Morales et al., PLASMA-MEMBRANE LOCALIZATION OF G-ALPHA(Z) REQUIRES 2 SIGNALS, Molecular biology of the cell, 9(1), 1998, pp. 1-14
Citations number
51
Categorie Soggetti
Cell Biology",Biology
ISSN journal
10591524
Volume
9
Issue
1
Year of publication
1998
Pages
1 - 14
Database
ISI
SICI code
1059-1524(1998)9:1<1:PLOGR2>2.0.ZU;2-I
Abstract
Three covalent attachments anchor heterotrimeric G proteins to cellula r membranes: the alpha subunits are myristoylated and/or palmitoylated , whereas the gamma chain is prenylated. Despite the essential role of these modifications in membrane attachment, it is not clear how they cooperate to specify G protein localization at the plasma membrane, wh ere the G protein relays signals from cell surface receptors to intrac ellular effector molecules. To explore this question, we studied the e ffects of mutations that prevent myristoylation and/or palmitoylation of an epitope-labeled alpha subunit, alpha(z). Wild-type alpha(z) (alp ha(z)-WT) localizes specifically at the plasma membrane. A mutant that incorporates only myristate is mistargeted to intracellular membranes , in addition to the plasma membrane, but transduces hormonal signals as well as does alpha(z)-WT. Removal of the myristoylation site produc ed a mutant alpha(z) that is located in the cytosol, is not efficientl y palmitoylated, and does not relay the hormonal signal. Coexpression of beta gamma with this myristoylation defective mutant transfers it t o the plasma membrane, promotes its palmitoylation, and enables it to transmit hormonal signals. Pulse-chase experiments show that the palmi tate attached to this myristoylation-defective mutant turns over much more rapidly than does palmitate on alpha(z)-WT, and that the rate of turnover is further accelerated by receptor activation. In contrast, r eceptor activation does not increase the slow rate of palmitate turnov er on alpha(z)-WT. Together these results suggest that myristate and b eta gamma promote stable association with membranes not only by provid ing hydrophobicity, but also by stabilizing attachment of palmitate. M oreover, palmitoylation confers on alpha(z) specific localization at t he plasma membrane.