PI3K RBD (Phosoinositide 3-kinase Ras Binding domain), is a domain found in PI3K molecules that binds to the Ras protein which is key to intracellular signalling. Activated Ras will bind to p110 subunit activating PI3K alpha. To a lesser extent Ras will also activate PY3K gamma .
PI3Ks (phosphatidylinositol 3-kinases) are lipid kinases. They phosphorylate 4,5-bisphonate which then initiates a variety of signaling events. They have been grouped into three different classes; Class I, Class II and Class III. Class I PI3Ks are heterodimers that consist of a p110 catalytic subunit and a regulatory subunit (these are of the p85 or the p101 type). All catalytic subunits have an N-terminal adaptor-binding domain that binds to p85, a Ras- binding domain (RBD), a putative membrane-binding domain (C2), a helical domain of unknown function, and a kinase catalytic domain. Class II PI3Ks do not possess the ABD domain and they are characterised by a carboxy terminal C2 domain and Class III enzymes do not have eithrt the ABD or the RBD domains; hence it is possible to distingush the three different classes of PI3Ks. 
- ↑ RAS binding domain(Author unknown) http://www.mrc-lmb.cam.ac.uk/rlw/text/pi3k%20web%20pages/rbd.html. Accessed 24/10/2012.
- ↑ http://www.ebi.ac.uk/interpro/entry/IPR000341(accessed 20/10/14)