Abstract
Regulation of cellular response to external stimuli, hormones and neurotransmitters, is an important mechanism for controlling cellular functions. The transmembrane signaling of the hormone receptors is regulated by GTP-binding proteins and their associated proteins. A new class of GTP-binding protein, Gαh is a bifunctional enzyme possessing two biological functions, namely GTPase and transglutaminase (TGase) activity. This bifunctional Gαh mediates the α1B-adrenoceptor signal to an 85- kDa phospholipase C-δ1 (PLC-δ1) and associates with a -50 kDa protein (Gβh) which regulates the the GTP/GDP binding affinity of Gαh. Gh, the holoenzyme is thus a heterodimer, and the subunits dissociate from each other upon activation with GTP or its analogues. The GTPase and TGase activities of Gαh are regulated by two reciprocal activators, Ca2+ and GTP. The GTP-binding subunit, Gαh directly interacts with the α1B-adrenoceptor and stimulates PLC-δ1. Gβh, however, neither interacts with the receptor nor stimulates PLC-δ1. Therefore, Gβh functions as a counterpart to the receptor for the activation of Gαh.
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Im, MJ. Biological functions of the unusual guanine nucleotide-binding protein Gαh: transglutaminase II. Exp Mol Med 28, 109–117 (1996). https://doi.org/10.1038/emm.1996.17
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DOI: https://doi.org/10.1038/emm.1996.17