Shibire mutants
Shibire is a temperature sensitive phenotype in Drosophila that results in paralysis at the non-permissive temperature that is reversed on lowering to the permissive temperature. The phenotype is the result of the inability of endocytic vesicles to be separated from the parent membranes and thus there is a depletion of vesicles especially in synaptic terminals.


Larger movie of mutations (6.8MB)
Shibire ts1 (G273D): One can see in the structure above that this residue is on a tight bend. Mutations are likely to destabilise helix alpha5 and perhaps even the coordination of GTP. It is not clear why the ts1 mutation works at lower temperatures. The same mutation in mammalian dynamin I does not give a clear WT phenotype at the non-restrictive temperature.
Shibire ts2 (G148S) is in the Switch2 region of dynamin. This region is not resolved in the DymA structure but the comformation of this loop will be necessary for GTP binding and hydrolysis. It is quite likely that this mutation is not a global unfolding mutant at the non-permissive temperature. The T141 and K142 mutants in bovine dynamin are on this same loop and are necessary for mechanochemical coupling (see Marks et al 2001).

P62S is a temperature sensitive mutant in C.elegans. It is found at the end of the G2 binding loop and thus a mutant of Proline to Serine will disrupt the conformation of this loop and thus the coordination of Mg.

The above movie (from Bing Zhang's lab in UT Austin) shows a temperature shift experiment on Shibire and WT flies. Paralysis is first observed when the flies fall to the bottom of the vial. The onset is very quick and it is reversible as long as the temperature shift is not maintained for a long time.
(larger movie.mov)(large movie.mpg)

References:
Suzuki et al 1971, Grigliatti et al 1973, Poodry and Edgar 1979, Koenig and Ikeda 1989, van Dam and Stoorvogel 2002

Back to GTPase domain
Back to Dynamin Home Page