H. Nakaoka et al., G(H) - A GTP-BINDING PROTEIN WITH TRANSGLUTAMINASE ACTIVITY AND RECEPTOR SIGNALING FUNCTION, Science, 264(5165), 1994, pp. 1593-1596
The alpha(1)-adrenergic receptors activate a phospholipase C enzyme by
coupling to members of the large molecular size (approximately 74 to
80 kilodaltons) G alpha(h) family of guanosine triphosphate (GTP)-bind
ing proteins. Rat liver G alpha(h) is now shown to be a tissue transgl
utaminase type II (TGase II). The transglutaminase activity of rat liv
er TGase II expressed in COS-1 cells was inhibited by the nonhydrolyza
ble GTP analog guanosine 5'-O-(3-thiotriphosphate) or by alpha(1)-adre
nergic receptor activation. Rat liver TGase II also mediated alpha(1)-
adrenergic receptor stimulation of phospholipase C activity. Thus, G a
lpha(h) represents a new class of GTP-binding proteins that participat
e in receptor signaling and may be a component of a complex regulatory
network in which receptor-stimulated GTP binding switches the functio
n of G alpha(h) from transglutamination to receptor signaling.