Introduction

What are Rabs?

Rabs are members of the Ras super-family of small GTP binding proteins. 

They are responsible for the specificity of membrane trafficking, targeting vesicles to their specified membrane.  This is done by having different Rabs working in different areas of trafficking.

Fig 1. GTP molecule. 

Image courtesy of Wki Commons under the creative commons licence

What are small GTP binding proteins?

Small monomeric 21kDa proteins with intrinsic GTPase activity that can bind to and hydrolyse GTP.  Binding of GTP causes a structural change in the "switch" region of small GTP binding proteins, altering the protein resulting in its activation.  Hydrolysis of the GTP resets the switch region and turns the protein "off". 

Usually, various accessory proteins interact with the GTPase to modulate this process by speeding it up, slowing it down or activating the process.

Many GTPases, including Rabs, have post-translational lipid modifications to target them to specific membrane sites.

Mutations in the Rab transport pathways can result in various tissue specific diseases, including Choroideremia and Griscelli Syndrome type 2.

Header image courtesy of flickr under the creative commons licence