Fatty acylation of proteins: new insights into membrane targeting of myristoylated and palmitoylated proteins.

▪ Abstract GTPase-activating proteins (GAPs) regulate heterotrimeric G proteins by increasing the rates at which their α subunits hydrolyze bound GTP and thus return to the inactive state. G protein GAPs act allosterically on Gα subunits, in contrast to GAPs for the Ras-like monomeric GTP-binding proteins. Although they do not contribute directly to the chemistry of GTP hydrolysis, G protein GAPs can accelerate hydrolysis >2000-fold. G protein GAPs include both effector proteins (phospholipase C-β, p115RhoGEF) and a growing family of regulators of G protein signaling (RGS proteins) that are found throughout the animal and fungal kingdoms. GAP activity can sharpen the termination of a signal upon removal of stimulus, attenuate a signal either as a feedback inhibitor or in response to a second input, promote regulatory association of other proteins, or redirect signaling within a G protein signaling network. GAPs are regulated by various controls of their cellular concentrations, by complex interactions wit...

GTPase-Activating Proteins for Heterotrimeric G Proteins: Regulators of G Protein Signaling (RGS) and RGS-Like Proteins

This review is concerned with the structures and mechanisms of a superfamily of regulatory GTP hydrolases (G proteins). G proteins include Ras and its close homologs, translation elongation factors, and heterotrimeric G proteins. These proteins share a common structural core, exemplified by that of p21ras (Ras), and significant sequence identity, suggesting a common evolutionary origin. Three-dimensional structures of members of the G protein superfamily are considered in light of other biochemical findings about the function of these proteins. Relationships among G protein structures are discussed, and factors contributing to their low intrinsic rate of GTP hydrolysis are considered. Comparison of GTP- and GDP-bound conformations of G proteins reveals how specific contacts between the γ-phosphate of GTP and the switch II region stabilize potential effector-binding sites and how GTP hydrolysis results in collapse (or reordering) of these surfaces. A GTPase-activating protein probably binds to and stabiliz...

G PROTEIN MECHANISMS: Insights from Structural Analysis

ture that clearly identifies the specific enzyme isoform. A widely accepted nomenclature (3), which will be used in these Perspective articles, identifies the three mammalian enzyme isoforms as nNOS, iNOS, and eNOS, reflecting the tissues of origin for the original protein and cDNA isolates. As denoted by its prefix, nNOS was originally purified and cloned from neuronal tissues. However, nNOS is now known to be much more widely distributed, with an important level of expression in skeletal muscle. iNOS, originally purified and cloned from an immunoactivated macrophage cell line, has since been identified in myriad mammalian tissues, and iNOS expression has been studied in cells as diverse as cardiac myocytes, glial cells, and vascular smooth muscle cells (to name only a few). eNOS, the last of the three mammalian NOS isoforms to be isolated, was originally purified and cloned from vascular endothelium, but has since been discovered in cardiac myocytes, blood platelets, brain (hippocampus), and elsewhere. To add to the confusion, the human genes for the NOS isoforms are officially categorized in the order of their isolation and characterization; thus, the human genes encoding nNOS, iNOS, and eNOS are termed NOS1 , NOS2 , and NOS3 , respectively.

/pdf/nitric-oxide-synthases-which-where-how-and-why-1k44tfbri6.pdf

Nitric oxide synthases: which, where, how, and why?

LAT Palmitoylation: Its Essential Role in Membrane Microdomain Targeting and Tyrosine Phosphorylation during T Cell Activation

https://www.jbc.org/content/270/2/503.full.pdf

Lipid modifications of trimeric G proteins.

Palmitoylation is required for signaling functions and membrane attachment of Gq alpha and Gs alpha.

Three covalent attachments anchor heterotrimeric G proteins to cellular 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, where the G protein relays signals from cell surface receptors to intracellular effector molecules. To explore this question, we studied the effects of mutations that prevent myristoylation and/or palmitoylation of an epitope-labeled alpha subunit, alpha z. Wild-type alpha z (alpha 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 produced a mutant alpha z that is located in the cytosol, is not efficiently palmitoylated, and does not relay the hormonal signal. Coexpression of beta gamma with this myristoylation defective mutant transfers it to the plasma membrane, promotes its palmitoylation, and enables it to transmit hormonal signals. Pulse-chase experiments show that the palmitate 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, receptor activation does not increase the slow rate of palmitate turnover on alpha z-WT. Together these results suggest that myristate and beta gamma promote stable association with membranes not only by providing hydrophobicity, but also by stabilizing attachment of palmitate. Moreover, palmitoylation confers on alpha z specific localization at the plasma membrane.

Paul T. Wilson

Papers

Lipid modifications of trimeric G proteins.

Palmitoylation is required for signaling functions and membrane attachment of Gq alpha and Gs alpha.

Plasma Membrane Localization of Gαz Requires Two Signals

Fatty acylation of alpha z. Effects of palmitoylation and myristoylation on alpha z signaling.

The effect of eight V2 vasopressin receptor mutations on stimulation of adenylyl cyclase and binding to vasopressin.