Mastoparan activation of G proteins and NDPK.

Cornelius Krasel krasel at alf.biochem.mpg.de
Mon Feb 21 16:17:32 EST 1994


Matthew W Martin (ucgbmwm at ucl.ac.uk) wrote:
:  Mastoparan, a component of wasp venom, has been shown to activate
: the heterotrimeric GTP-binding protein (G protein), Go - and other
: G proteins (Higashijima, et al; 1988; J. Biol. Chem.; 263; 6491-6494).

:  Does anyone know if there is any evidence (published or not) about
: the effect of this peptide on monomeric GTP-binding proteins?

I don't know.

:  I'd like to get a discussion started here about how this peptide 
: activates G proteins.

Well, the mainstream hypothesis is that Mastoparan somehow is able to mimic
the activated receptor. Mastoparan shows a high level of amphiphilicity (sp?)
and therefore it was assumed that receptors would also signal through
peptides which could form amphiphilic helices. While it seems to be important
for Mastoparan derivatives to be able to form amphiphilic alpha-helices
(see e.g. Higashijima et al. 1990: J. Biol. Chem. 265, 14176--14186;
Danilenko et al. 1993: Biochem. Biophys. Res. Comm. 196, 1296--1302) this
seems not necessarily to be the case for receptors: Voss et al. (1993:
J. Biol. Chem. 268, 4637--4642) tested the ability of six peptides
derived from the third intracellular loops of the D1 dopamine, D2 dopamine
and beta1-adrenergic receptors (which are supposed to interact with
G proteins). Only one of these peptides was able to stimulate the
effector G protein, but it did apparently not form an amphipathic
alpha helix.

To further complicate matters, in a recent issue of the Biochemical Journal
there was a publication of the group of Guenther Schultz (Berlin, FRG)
who have shown that certain substances such as artificial sweeteners
(saccharine) and others, e.g. chinin, are also able to activate
G proteins in vitro. I have to read this article yet but off-hand
it seems to be difficult to understand these results in the light
of the "amphipathic helix" theory.

: Afterall, isn't a good discussion the TRUE
: PURPOSE of News Groups?

I fully agree :-)

--Cornelius.

--
/* Cornelius Krasel, Abt. Lohse, Genzentrum, D-82152 Martinsried, Germany */
/* email: krasel at alf.biochem.mpg.de                 fax: +49 89 8578 3795 */
/* "People are DNA's way of making more DNA." (Edward O. Wilson, 1975)    */



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