Structure
Ras contains a six-stranded beta sheet and 5 alpha helices:
- G domain (166 amino acids) which binds guanosine nucleotides, about 20kDa.
- C terminal membrane targeting region (CAAX-COOH, also known as CAAX box) which is lipid-modified by farnesyl transferase, RCE1 and ICMT
The G domain contains five G motifs that bind GDP/GTP directly
- G1 - P-loop binds the beta phosphate of GDP and GTP
- G2 - threonine-35 also switch 1, binds the terminal phosphate of GTP, but makes no contacts with GDP
- G3 - DXXG motif, aspartate-57 is specific for guanine rather than adenine
- G4 - LVGNKxDL motif
- G5 - SAK consensus sequence, the alanine-146 is specific for guanine rather than adenine
and two switches which are the main parts of the protein that move upon activation by GTP.
- switch I includes threonine-35
- switch II glycine-60 in DXXG motif
Ras also binds a magnesium ion which helps to coordinate nucleotide binding.
Read more about this topic: Ras Subfamily
Famous quotes containing the word structure:
“I’m a Sunday School teacher, and I’ve always known that the structure of law is founded on the Christian ethic that you shall love the Lord your God and your neighbor as yourself—a very high and perfect standard. We all know the fallibility of man, and the contentions in society, as described by Reinhold Niebuhr and many others, don’t permit us to achieve perfection.”
—Jimmy Carter (James Earl Carter, Jr.)
“Communism is a proposition to structure the world more reasonably, a proposition for changing the world. As such, we have to analyze it and, if we deem it reasonable, act upon it.”
—Friedrich Dürrenmatt (1921–1990)
“When a house is tottering to its fall,
The strain lies heaviest on the weakest part,
One tiny crack throughout the structure spreads,
And its own weight soon brings it toppling down.”
—Ovid (Publius Ovidius Naso)