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Activating and de-activating Ras
Key human members of Ras family
KRAS, HRAS, NRAS Kick-start cell growth when activated Other signaling?
Some terms
Conserved proteins, genes, etc.: Appear in many organisms, presumably “conserved” by evolution
Allosteric site: a site (other than the catalytic site) that affects the rate of a catalytic reaction
Hydrolysis: cleavage of chemical bonds by the addition of water
GTPase: a protein that catalyzes hydrolysis of GTP to GDP
A Video: GTPases as Molecular Switches
Turning Ras On and Off
Ras is normally tightly bound to GDP Ras is activated by binding to GTP instead of GDP Ras is a weak GTPase (i.e., it encourges hydrolysis of
GTP into GDP) A “guanine nucleotide exchange factor” helps Ras to
exchange GTP for GDP GEF is the generic term Sos1 is the specific GEF we will look at
A GTPase Activating Protein speeds up Ras GTPase activity
GAP is the generic term RASA1 is the specific GAP we will look at
Turning Ras On and Off
Ras-GDP
Ras-GDP is the “off” state of Ras
Turning Ras On and Off
Ras-GDP
Ras-GTP
Ras-GTP is the “on” state of Ras
Turning Ras On and Off
Ras-GDP
Ras-GTP
The entire reversible reaction (????)
Turning Ras On and OffGDP
GTP
Ras-GDP
Ras-GTP
Ras-O
Ras can bind to either GDP or GTP (or not at all)
Turning Ras OnGDP
GTP
Ras-GDP
Ras-GTP
Ras-OGEF
A guanine nucleotide exchange factor (GEF) helps Ras exchange a GDP for a GTP
Turning Ras On and OffGDP
GTP
GAP
Ras-GDP
Ras-GTP
Ras-OGEF
A GTPase Activating Protein (GAP) helps Ras turn the GTP back into GDP
But wait: There’s More!!
GEF
Ras-GDP
Ras-GTP
GAP
How Fast Does Ras Turn On?
Sos1
Ras-GDP
Ras-GTP
Cdc25
REM
Guanine Nucleotide Exchange Rate
Ras-GDP
Sos1
Rate: kcat, Km
Part of Sos1
Ras-GDP
Cdc25
REM
Guanine Nucleotide Exchange Rate
Sos1
Rate: kcat, Km
Part of Sos1
Ras-GDP
GDP
Ras-O
Cdc25
REM
Guanine Nucleotide Exchange Rate
Ras-O
Ras-GTP
Sos1
GTP
Rate: kcat, Km
Part of Sos1
Cdc25
REM
Guanine Nucleotide Exchange Rate
Ras-GDP
Ras-O
Ras-GTP
Sos1
GDPGTP
Part of Sos1
Cdc25
REM
Guanine Nucleotide Exchange Rate
Ras-GDP
Ras-O
Ras-GTP
Sos1
GDPGTP
Rate: 5 times as fast
Ras-GDP
Part of Sos1
Cdc25
REM
Guanine Nucleotide Exchange Rate
Ras-GDP
Ras-O
Ras-GTP
Sos1
GDPGTP
Rate: 75 times as fast
Ras-GTP
Part of Sos1
Ras Deactivation (Hydrolysis)
Ras-GDP
Ras-GTP
RASA1
How Fast Does Ras Turn Off
Ras-GDP
Ras-GTP
Ras-GTP is a GTPase: It hydrolyzes GTP to GDP (slowly)
Ras Deactivation (Hydrolysis)
Ras-GDP
Ras-GTP
RASA1
RASA1 speeds up the hydrolysis by ???
Turning Ras On and Off: The Whole Story (… or is it?)
GDP
GTP
RASA1
Ras-GDP
Ras-GTP
Ras-O
Sos1
slow
fast
Super fast
Summary
Ras is normally tightly bound to GDP Ras is activated by binding to GTP instead of GDP A “guanine nucleotide exchange factor” helps Ras to
exchange GTP for GDP GEF is the generic term Sos1 is the specific GEF we will look at Sos1 has an allosteric site that affects the reaction rate
A GTPase activating protein speeds up Ras GTPase activity (ie, hydrolyzing the GTP so it becomes GDP)
GAP is the generic term RASA1 is the specific GAP we will look at
YouTube Lectures on Ras
Wittinghofer Part 1 Wittinghofer Part 2