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Molecular and Cellular Biology, April 2003, p. 2476-2488, Vol. 23, No. 7
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.7.2476-2488.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

GGAPs, a New Family of Bifunctional GTP-Binding and GTPase-Activating Proteins

Chunzhi Xia,1 Wenbin Ma,1 Lewis Joe Stafford,1 Chengyu Liu,1 Liming Gong,2 James F. Martin,1 and Mingyao Liu1*

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,1 Department of Cardiology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 770302

Received 30 July 2002/ Returned for modification 11 September 2002/ Accepted 30 December 2002

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.

* Corresponding author. Mailing address: Center for Cancer Biology and Nutrition, Alkek Institute of Biosciences and Technology, Texas A&M University System Health Science Center, 2121 West Holcombe Blvd., Houston, TX 77030. Phone: (713) 677-7505. Fax: (713) 677-7512. E-mail: mliu{at}ibt.tamu.edu.

Molecular and Cellular Biology, April 2003, p. 2476-2488, Vol. 23, No. 7
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.7.2476-2488.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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