Guanine Nucleotide-Binding Proteins (G-proteins¨)

G-proteins

Guanine Nucleotide-Binding Proteins

bind guanine nucleotides

• GDP

• GTP

GTP to GDP

GTP can be hydrolyzed by loss of phosphate into GDP

G-proteins have enzymatic activity that catalyze hydrolysis

GTPase activity

enzymatic activity in G-proteins that catalyze hydrolysis of GTP to GDP

G-proteins binding conditions

G-proteins must release GDP to bind to another GTP molecule

G-protein binding affinity

will bind to GTP if concentration is high enough

in cells GTP concentration usually much higher than GDP concentration, which means G-protein much more likely to bind to GTP

G-protein conformation

Active:

GTP-bound form of G-protein, has different conformation than

Inactive form:

GDP-bound form

form with no nucleotide

GAPs

GTPase Activating Protein

regulate activity of G-protein

stimulate hydrolysis of GTP into GDP by G-protein

favor inactive state

GEPs

Guanine Nucleotide Exchange Factors

stimulate release of GDP by G-protein

leads to empty G-protein, which can bind to GTP

favor active state of G-protein

G-proteins act like

molecular switches

can be on/off

can be quickly switched between on/off states

key for temporal and spatial recognition of cellular processes

G-proteins catalyze

GTP hydrolysis

GTP-bound state

active conformation

GDP-bound state

inactive conformation

GAPs

stimulate GTP hydrolysis/inactive state

GEFs

stimulate GDP release/active state