G-proteins and signal transduction

Cornelius Krasel krasel at wpxx02.toxi.uni-wuerzburg.de
Fri Mar 14 11:09:29 EST 1997

ylee at REED.EDU wrote:
> Hello, I am a hapless biology undergraduate reading about signal
> transduction and second messengers.  Can anyone out there explain why
> G-proteins and Ca2+ play such a diverse role in cellular regulation and
> signal transduction?  i haven't found any information on that in the
> literature.

This is somewhat surprising since there is a vast literature on this

G-proteins consist of alpha and beta-gamma subunits (the beta- and
gamma-subunit, once associated, cannot dissociate again and are
viewed as a functional entity). There are five families of G-proteins:
Gs, stimulating adenylyl cyclase and possibly activating certain
channels; Gi/o, inhibiting adenylyl cyclase amongst other things;
Gq/11, coupling to PLC; G12/13, the effectors of which are not really
delineated yet; and Gz. beta-gamma subunits have also been found to
activate adenylyl cyclase, PLC, a wide variety of channels, GRKs,
certain PI3-kinase isoenzymes and others.

PLC activation leads to hydrolysis of PIP2 into DAG and IP3 which will
increase the intracellular Ca2+ level. Ca2+ binds to various proteins,
amongst them calmodulin which in turn can affect the activity of a
wide variety of enzymes.

In effect, the signals from a wide variety of receptors (there are
definitely more than 200 sequences of G-protein coupled receptors
in the database) converge in a relatively small pool of G-proteins
(although there are some 5 beta and 12 gamma subunits out there, it
appears that most combinations are of similar selectivity in vitro)
activating then a large variety of effects:

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/* Cornelius Krasel, U Wuerzburg, Dept. of Pharmacology, Versbacher Str. 9 */
/* D-97078 Wuerzburg, Germany   email: phak004 at rzbox.uni-wuerzburg.de  SP3 */
/* "Science is the game we play with God to find out what His rules are."  */

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