title: GGAPs, a new family of bifunctional GTP-binding and GTPase-activating proteins.
abstract: G proteins are molecular switches that control a wide variety of physiological functions, including neurotransmission, transcriptional activation, cell migration, cell growth. and proliferation. The ability of GTPases to participate in signaling events is determined by the ratio of GTP-bound to GDP-bound forms in the cell. All known GTPases exist in an inactive (GDP-bound) and an active (GTP-bound) conformation, which are catalyzed by guanine nucleotide exchange factors and GTPase-activating proteins (GAPs), respectively. In this study, we identified and characterized a new family of bifunctional GTP-binding and GTPase-activating proteins, named GGAP. GGAPs contain an N-terminal Ras homology domain, called the G domain, followed by a pleckstrin homology (PH) domain, a C-terminal GAP domain, and a tandem ankyrin (ANK) repeat domain. Expression analysis indicates that this new family of proteins has distinct cell localization, tissue distribution, and even message sizes. GTPase assays demonstrate that GGAPs have high GTPase activity through direct intramolecular interaction of the N-terminal G domain and the C-terminal GAP domain. In the absence of the GAP domain, the N-terminal G domain has very low activity, suggesting a new model of GGAP protein regulation via intramolecular interaction like the multidomain protein kinases. Overexpression of GGAPs leads to changes in cell morphology and activation of gene transcription.
authors.affiliation: Center for Cancer Biology and Nutrition, Alkek Institute of Biosciences and Technology, and Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, Houston, Texas 77030, USA.
authors.forename: Chunzhi
authors.initials: C
authors.lastname: Xia
authors.forename: Wenbin
authors.initials: W
authors.lastname: Ma
authors.forename: Lewis Joe
authors.initials: LJ
authors.lastname: Stafford
authors.forename: Chengyu
authors.initials: C
authors.lastname: Liu
authors.forename: Liming
authors.initials: L
authors.lastname: Gong
authors.forename: James F
authors.initials: JF
authors.lastname: Martin
authors.forename: Mingyao
authors.initials: M
authors.lastname: Liu
mesh_terms: D020727:ADP-Ribosylation Factors; D000595:Amino Acid Sequence; D000818:Animals; D017089:Ankyrin Repeat / Q000235:genetics; D001798:Blood Proteins / Q000235:genetics; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000145:classification* / Q000235:genetics*; D020690:GTPase-Activating Proteins / Q000096:biosynthesis / Q000145:classification* / Q000235:genetics*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D009928:Organ Specificity; D010750:Phosphoproteins / Q000235:genetics; D010802:Phylogeny; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D018631:ras Proteins / Q000235:genetics
chemical_list: C470574:AGAP1 protein, human; D001798:Blood Proteins; D020690:GTPase-Activating Proteins; D010750:Phosphoproteins; C039077:platelet protein P47; C485997:AGAP2 protein, human; C472718:AGAP3 protein, human; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors; D018631:ras Proteins