Immunological demonstration of G_q-protein inLimulusphotoreceptors

Abstract

The phototransduction cascade in invertebrates involves the coupling of rhodopsin activation to the action of the enzyme phospholipase C. This step is performed by G-proteins. An antibody against the a-subunit of a mouse G q type G-protein recognized protein bands in Western blots of lateral eye and ventral nerve photoreceptors of Limulus. The protein bands had an apparent molecular mass of about 42 kDa. The antibody also recognized protein bands of a similar molecular mass in immunoblots of brain and intestine tissue. Immunoreactivity was found in lateral eye frozen sections where it was confined to the rhabdom region. When the antibody was applied to ultrathin sections of ventral nerve photoreceptors, the highest density of labeling was found on the rhabdomeral microvilli, but gold particles were also scattered in the cytoplasm. We conclude that a G-protein of the type G q participates in the phototransduction of Limulus.

Immunocytochemical localization of opsin, visual arrestin, myosin III, and calmodulin in Limulus lateral eye retinular cells and ventral photoreceptors

“…An extensive literature details the physiology (Smith et al, 1965; Mellecchia et al, 1966; recently reviewed in Dorlöchter and Stieve, 1997) and ultrastructure (Miller, 1957; Clark et al, 1969; Fahrenbach, 1969, 1975; Calman and Chamberlain, 1982b; Chamberlain and Barlow, 1984; Herman 1991a,b) of these photoreceptors. However, relatively little is known about their biochemical organization, largely because few antibodies specific for Limulus photoreceptor proteins have been characterized (Calman and Chamberlain, 1982a; Jinks et al, 1996; Munger et al, 1997; Dorlöchter et al, 1997; Ukhanov et al, 1998; Battelle et al, 1998). Information as essential as the distribution of opsin is lacking for these cells.…”

The excitation cascade of Limulus ventral photoreceptors: guanylate cyclase as the link between InsP3-mediated Ca2+release and the opening of cGMP-gated channels

“…Metarhodopsin is inactivated in less than 150 ms [37]; while active about 10 G proteins are turned on [38]. The G protein involved has been identified as G q in Limulus [39,40]. In the next stage of the cascade, PLC is activated by G q , resulting in the hydrolysis of phosphatidyl inositol-4,5-bisphosphate to produce InsP 3 and diacyglycerol.…”

Immunolocalization of a Gαq protein to the chemosensory organs of Dipolydora quadrilobata (Polychaeta: Spionidae)

“…To examine the distribution of Gαq protein in cellular structures of D. quadrilobata by transmission electron microscopy (TEM), we modified methods used by Dorlöchter et al (1997). Worms were relaxed in magnesium chloride and fixed overnight in 4% paraformaldehyde, 0.25% glutaraldehyde in 0.1 M cacodylate buffer pH 7.6 at 4°C.…”