Ras Protein and Pancreas Cancer: Difference between revisions

Ras proteins are the founding members of a large superfamily of monomeric small GTPases. These proteins are best known for their ability to serve as molecular switches regulating diverse cellular processes that include cell cycle progression, cell survival, actin cytoskeletal organization, cell polarity and movement, and vesicular and nuclear transport <ref name='Gervaise'>doi:10.1002/bip.22840</ref>. Both unicellular and multicellular organisms express Ras proteins. The human Ras superfamily is divided into five major branches: Ras proteins, Rho, Ran, Rab, and “unclassified” sequences (Gervaise Loirand, 2013). Even though, these are separated branches, they share a lot of similarities not only in their structure but also in their functions.  

Proteins are structured with alpha helices and beta sheets, in this case Ras proteins are made up of five alpha helices and 6 beta sheets. The diphosphate-binding loop G1 (also known as P-loop), with the consensus sequence, connects the β1 strand to the α1 helix and contacts the α- and βphosphates of the guanine nucleotide. The connection between the α1 helix and the β2 strand corresponds to G2 and contains a conserved threonine residue (Thr35) involved in Mg2+coordination. The G3 domain, at the NH2 terminus of the α2 helix, links the sites for binding Mg2+ and the γ-phosphate of GTP. The G4 domain that links the β5 strand and the α4 helix recognizes the guanine ring. The G5 loop, located between β6 and helix α5, reinforces the guanine base recognition site (Gervaise Loirand, 2013). Ras proteins act as connectors which connect the interior of the cell with the cell surface (Gervaise Loirand, 2013). The binding to GTP and GDP determines whether they are activated or not, they undergo a conserved mechanism: Ras functions require the participation of distinct regulatory proteins to control the GDP/GTP cycling rate (Gervaise Loirand, 2013). Indeed, the extent and duration of Ras activation in cells depends on the interplay between a variety of negative and positive regulators of the Ras cycle (Gervaise Loirand, 2013).  

2013https://doi.org/10.1152/physrev.00021.2012