The regulatory components of adenylate cyclase and transducin. A family of structurally homologous guanine nucleotide-binding proteins.

D R Manning,A G Gilman

doi:10.1016/s0021-9258(18)32332-9

Abstract

G/F and transducin are guanine nucleotide-binding regulatory proteins that mediate activation of adenylate cyclase and of a rod outer segment cyclic GMP-specific phosphodiesterase, respectively. The substrate for islet-activating protein is a third guanine nucleotide-binding protein that is postulated to mediate inhibition of adenylate cyclase. The extent of structural homology among subunits of all three proteins was examined by analyses of amino acid compositions and electrophoretic patterns of proteolytic peptides. The lower molecular weight subunits (beta subunits; Mr = 35,000) of these proteins have identical amino acid compositions and yield similar peptides upon proteolysis with Staphylococcus aureus V8 protease and elastase. The higher molecular weight subunits (alpha subunits; Mr = 39,000, 41,000, and 45,000) are also similar to each other in these respects. Similarity between the subunits of transducin and the islet-activating protein (IAP) substrate is especially evident. Substantial differences do, however, exist between the lower and higher molecular weight subunits within each protein. In addition, evidence was obtained that the 41,000-Da subunit of the IAP substrate is not derived from the 45,000-Da subunit of G/F. It is concluded that transducin, the IAP substrate, and G/F represent a family of structurally homologous guanine nucleotide-binding regulatory proteins.

Highlights

G/F and transducin are guanine nucleotide-binding component of adenylate cyclase
The higher molecular weight subunits(asubunits; brane-bound protein appears to correlate with the effect of the toxin to block inhibition of adenylate cyclase by appropriate neurohormones [19,20,21], it has been hypothesized that the substratefor IAP is the guanine nucleotide-binding inhibitory regulator of adenylate cyclase [18, 21]
Evidence was obtained that the41,000-Da guanine nucleotides [5] and, in this state, canactivate the subunit of the IAP substrate is not derived from the catalytic component of adenylate cyclase in the absence of

Summary

A FAMILY OF STRUCTURALLY HOMOLOGOUS GUANINE NUCLEOTIDE-BINDING PROTEINS*

It is concluded that trans- the 35,000-Da p~lypeptide.~ T3h5e,000-Da subunit is postuducin, the IAP substrate, and G F represent a family lated to inhibit activation of adenylate cyclase as a result of of structurallyhomologous guanine nucleotide-binding its reversible association with the higher molecular weight regulatory proteins. The stimulatory regulator of adenylate cyclase is the siteof 41,000-Da subunit [18].The 41,000-Dasubunit binds guanine action of bothguanine nucleotides and fluoride and is, in nucleotides and is ADP-ribosylated by IAP. The latter modiaddition, a substrate for ADP-ribosylation catalyzed by chol- fication presumably results in attenuation of hormonal inhiera toxin [5,9,10,11]. Protein was assayedby staining with Amido black [36]

RESULTS

LEU VAL MET I L E

DISCUSSION