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. 1994 Aug 1;312(2):474-9.
doi: 10.1006/abbi.1994.1334.

Heterotrimeric GTP-binding proteins (G proteins) and ADP-ribosylation factor (ARF) regulate priming of endosomal membranes for fusion

J M Lenhard  1 , M I Colombo, P D Stahl
Affiliations

Heterotrimeric GTP-binding proteins (G proteins) and ADP-ribosylation factor (ARF) regulate priming of endosomal membranes for fusion

J M Lenhard et al. Arch Biochem Biophys. .

Abstract

An in vitro assay that measures endosome fusion was used to characterize the role of guanosine triphosphate (GTP)-binding proteins in endocytosis. Guanosine 5',3-(thio)triphosphate (GTP gamma S), a nonhydrolyzable analog of GTP, stimulates the binding of cytosolic factors to the endosomal membrane (priming). GTP gamma S also enhances vesicle aggregation, resulting in the formation of an intermediate that is resistant to dilution. In this report we demonstrate that priming precedes the appearance of a dilution-resistant intermediate. Thus, GTP-binding proteins are involved in multiple sequential events preceding endosome fusion. Both heterotrimeric G proteins (G proteins) and ADP-ribosylation factors (ARFs) are GTP-binding proteins that regulate undefined steps involved in endocytosis. The addition of G beta gamma subunits of G proteins to the in vitro fusion assay resulted in inhibition of priming. In contrast, addition of ARF to the assay enhanced priming. Thus, heterotrimeric G proteins and ARF may regulate endocytosis by mediating the binding of cytosolic factor(s) required for fusion to the endosomal membrane. Taken together, the results show that multiple GTP-binding proteins regulate a series of distinct biochemical events required for endosome fusion.

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