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:
“Women over fifty already form one of the largest groups in the population structure of the western world. As long as they like themselves, they will not be an oppressed minority. In order to like themselves they must reject trivialization by others of who and what they are. A grown woman should not have to masquerade as a girl in order to remain in the land of the living.”
—Germaine Greer (b. 1939)
“Science is intimately integrated with the whole social structure and cultural tradition. They mutually support one other—only in certain types of society can science flourish, and conversely without a continuous and healthy development and application of science such a society cannot function properly.”
—Talcott Parsons (1902–1979)
“If rightly made, a boat would be a sort of amphibious animal, a creature of two elements, related by one half its structure to some swift and shapely fish, and by the other to some strong-winged and graceful bird.”
—Henry David Thoreau (1817–1862)