G-proteins

Abbreviation for "guanine nucleotide-binding proteins". G proteins occupy a key position in the signal transduction between receptor and second messenger systems.

A distinction is made between membrane-bound heterotrimeric G-proteins and cytosolic, monomeric, so-called "small" G-proteins.

• Heterotrimeric G proteins consist of 3 subunits (α, β and γ). They occupy a key position in signal transduction and are responsible for physiological (e.g. sight, smell, blood pressure regulation etc.) and pathophysiological effects (e.g. arterial hypertension).
• Small G proteins (monomers) (20-40 kDa; > 100 different small G proteins are known) are divided into 5 families: Ras, Rho, Rab, Sar1/Arf and Ran. Small G-proteins are involved in the regulation of numerous cell functions:
• Regulation of gene expression (Ras and Rho)
• Regulation of the cytoskeleton (Rho)
• Regulation of vesicle transport (Rab and Sar1/Arf)
• Regulation of the transport between cytoplasm and nucleus (Ran).

1. Aktories K et al (2005) Bacterial cytotoxins: targeting eukaryotic switches. Nat Rev Microbiol 3: 397-410