Certain G protein alpha-subunits, components of the
G-protein Coupled Receptor (GPCR) signal transduction system, have been shown
to form tight complexes with the cytoskeletal protein tubulin. These G proteins activate the GTPase of
tubulin, increasing the dynamic behavior of microtubules. Further, at least in the case of Gsa, tubulin
appears to transactivate Gsa (directly passing GTP from tubulin
to the Ga subunit), which increases GPCR-independent activation of adenylyl cyclase. Studies in the Rasenick lab suggest that chronic
antidepressant treatment moves Gsa from a subcellular region
enriched in tubulin to one where Gsa becomes less associated with
tubulin. We seek to understand the
molecular basis for these poorly understood phenomena. Modeling studies suggest that the
'switch' regions of Gsa interact directly with the GTP-binding site of b-tubulin. In order to gain further insight the structural basis for
this behavior, we propose to exploit our ability to purify a complex of Gsa and tubulin
to initiate crystallization trials and determine the three-dimensional crystal
structure of the complex.
Grant support: NIH R21 DA 020568