Meta-Biol

• Pathways

VAV proteins exist in an auto-inhibitory state folded in such a way as to inhibit the GEF activity of its DH domain. This folding is mediated through binding of tyrosines in the acidic domain to the DH domain and through binding of the CH domain to the C1 region. Activation of VAV may involve at least three different events to relieve this auto-inhibition. Phosphorylation of the tyrosines in the acidic domain causes them to be displaced from the DH domain, binding of a ligand to the CH domain may cause it to release the C1 domain and binding of PIP3 to PH domain may alter its conformation. VAV1 is phosphorylated on Y174 in the acidic domain, and this is mediated by Syk and Src-family tyrosine kinases. Once activated, VAV1 is then involved in the activation of RAC and CDC42 downstream of FCGR.