Release of guanosine triphosphate binding protein alpha subunits from mouse myocardial membranes: basic properties and their alterations in acute murine Chagas disease

Abstract

Objective: The aim was to investigate the arrangement of heterotrimeric alpha beta gamma G proteins in myocardial membranes using GTP gamma S dependent release characteristics of their alpha subunits in acute murine Chagas disease.

Methods: The properties of GTP gamma S dependent alpha subunit release were monitored immunochemically as well as by cholera toxin and pertussis toxin catalysed [32P]ADP ribosylation.

Results: GTP gamma S, as opposed to other nucleotides, caused optimal and virtually instantaneous release of soluble 40 kDa [32P]ADP ribosylated protein in pertussis toxin treated membranes. When determined immunochemically, infection decreased both the sensitivity to GTP gamma S dependent release of alpha i subunits and appeared to facilitate the appearance of GTP gamma S dependent release of alpha i3. GTP gamma S also caused the release of soluble 45 and 40 kDa proteins as detected by cholera toxin-[32P]ADP ribosylated membranes and immunochemical analysis. With regard to cholera toxin-[32P]ADP ribosylated Gs substrates sensitive to GTP gamma S dependent release, infection (1) decreased the amount of 45 kDa alpha s protein, (2) increased the amount of 40 kDa protein, and (3) enhanced sensitivity to GTP gamma S. In contrast, there was no effect of infection on the magnitude or sensitivity to GTP gamma S dependent release of immunochemical alpha s.

Conclusions: The diverse characteristics of GTP gamma S dependent release of the very similar alpha subunits from myocardial membranes and their unique sensitivity to infection with T cruzi suggest that these very similar proteins are arranged within the plasma membrane in such a manner as to modify their biochemical behaviour.