REGULATION OF CELLULAR SIGNALS BY G-PROTEINS

Extracellular signals are transduced across the cell by the cell surfa ce receptors, with the aid of G-proteins, which act at a critical poin t of signal transduction and cellular regulation, Structurally, G-prot eins are heterotrimeric consisting alpha, beta and gamma subunits but in functionally active state they dissociate into alpha subunit couple d to GTP and as beta gamma dimer. G-proteins can be broadly divided in to two classes based on their sensitivity to pertussis toxin and chole ra toxin. Existence of various forms of each of the subunit allows mol ecular diversity in the subunit species of G-proteins, These subunits interact with a wide range of receptors and effecters, facilitated by post translational modification of their subunits, Different types of G-proteins mediate several signalling events in different parts of the body, This review summarizes the features of (i) structural and funct ional heterogenity among different subunits of G-proteins, (ii) intera ction of G-proteins and their subunits with effecters with specific ca ses of G-protein mediated signalling in olfaction, phototransduction i n the retina, pas and uas related transduction and (iii) disease condi tions associated with malfunctioning of G-proteins.