Question

whats the role of small G proteins,Ras? what's the role of small G protein, Rho, Rac and CDC42?

Answer 1

In addition to the heterotrimeric G proteins, other forms of G proteins play important roles in cell function. These proteins belong to a large superfamily often referred to as “small G proteins” based on their low M_r (20,000 to 35,000).

The small G proteins, like the heterotrimeric G proteins, bind guanine nucleotides, possess intrinsic GTPase activity and cycle through GDP- and GTP-bound forms .One unifying feature of the various classes of G protein is that the binding of GTP versus GDP dramatically alters the affinity of the protein for some target molecule, apparently by inducing a large conformational change. Small G proteins appear to function as molecular switches that control several cellular processes.

Examples of Small G Proteins

Class	Proposed cellular function
Ras	Signal transduction (control of growth factor and MAP-kinase pathways)
Rac, CDC42	Signal transduction (control of cellular stress responses and MAP-kinase pathways)
Rab	Localized to synaptic vesicles, where it reg- ulates vesicle trafficking and exocytosis??
Rho	Assembly of cytoskeletal structures (e.g.,actin microfilaments)??
ARF	ADP-ribosylation of G?s Assembly and function of Golgi complex
EFTU	Associated with ribosomes, where it reg-ulates protein synthesis??
Ran	Nuclear-cytoplasmic trafficking of RNA and protein??

Ras :

Ras is a family of related proteins which is expressed in all animal cell lineages and organs. All Ras protein family members belong to a class of protein called small GTPase and are involved in transmitting signals within cells (cellular signal transduction).

Rho :

The Rho family of GTPases is a family of small (~21 kDa) signaling G proteins, and is a subfamily of the Ras superfamily.

The members of the Rho GTPase family have been shown to regulate many aspects of intracellular actin dynamics, and are found in all eukaryotic kingdoms, including yeasts and some plants.

The Rho family of GTPases belong to the Ras superfamily of proteins, which consists of over 150 varieties in mammals. Rho proteins sometimes denote some members of the Rho family (RhoA, RhoB, and RhoC), and sometimes refers to all members of the family. This article is about the family as a whole.

In mammals, the Rho family contains 22 members. Almost all research involves the three most common members of the Rho family: Cdc42, Rac1 and RhoA.

Rho family member	Action on actin filaments
Cdc42	affects filopodia
Rac1	affects lamellipodia
RhoA	affects stress fibres

Rac

Regulation of NADPH oxidases: the role of Rac proteins. The family of NADPH oxidases (NOXes) plays an important role in the production of ROS in response to receptor agonists such as growth factors or inflammatory cytokines that signal through the Rho-like small GTPases Rac1 or Rac2.

CDC42 :

Cdc42, is a protein involved in regulation of the cell cycle. It is known to influence a variety of signaling events and cellular processes in a variety of organisms from yeast to mammals