Proteomic analysis of bovine brain G protein gamma subunit processing heterogeneity.
We characterized the variable processing of the G protein gamma subunit isoforms associated with bovine brain G proteins, a primary mediator of cellular communication. Ggamma subunits were isolated from purified brain G proteins and characterized by Edman sequencing, by MALDI MS, by chemical and/or enzymatic fragmentation assayed by MALDI MS, and by MS/MS fragmentation and sequencing. Multiple forms of six different Ggamma isoforms were detected. Significant variation in processing was found at both the amino termini and particularly the carboxyl termini of the proteins. All Ggamma isoforms contain a carboxyl-terminal CAAX motif for prenylation, carboxyl-terminal proteolysis, and carboxymethylation. Characterization of these proteins indicates significant variability in the normal processing of all of these steps in the prenylation reaction, including a new variation of prenyl processing resulting from cysteinylation of the carboxyl terminus. These results have multiple implications for intracellular signaling mechanisms by G proteins, for the role of prenyl processing variation in cell signaling, and for the site of action and consequences of drugs that target the prenylation modification.
Cook
Lana A
LA
Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
Schey
Kevin L
KL
Wilcox
Michael D
MD
Dingus
Jane
J
Ettling
Rebecca
R
Nelson
Troy
T
Knapp
Daniel R
DR
Hildebrandt
John D
JD
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D044388:GTP-Binding Protein gamma Subunits / Q000737:chemistry / Q000378:metabolism*; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism*; D040901:Proteomics; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D044388:GTP-Binding Protein gamma Subunits; D020033:Protein Isoforms