Yeasts membrane disruption

Physical and chemical genetic techniques have been used to enhance the permeability of yeast membranes. Permeabilizing agents, such as polymyxin B sulfate and polymyxin B nonapeptide, have been used to physically disrupt the integrity of yeast membranes (14). However, use of such chemical agents in drug screening is not ideal, because of the toxicity induced by polymyxin B treatment. 

Stimulus-evoked, calcium-dependent release of acetylcholine (ACh) from the cholinergic synapse normally occurs through the formation of a fusion complex between ACh-containing vesicles and the intracellular leaflet of the nerve terminal membrane (Amon et al., 2001). This synaptic vesicle fusion complex consists of several proteins of the SNARE family, including a 25 kDa synaptosomal associated protein (SNAP-25), vesicle-associated membrane protein (VAMP, or synaptobrevin), and the synaptic membrane protein syntaxin. Other SNARE proteins have been identified as components of membrane transport systems in yeast and mammals but have not been implicated as targets for BoNTs. Meanwhile, type A and E neurotoxins cleave SNAP-25 while types B, D, F, and G act on VAMP and type C1 toxin cleaves both syntaxin and SNAP-25. Neurotoxin-mediated cleavage of any of these substrates disrupts the processes involved in the exocytotic release of ACh and leads to flaccid paralysis of the affected skeletal muscles. 

Several types of evidence suggest that myosin V also participates In the Intracellular transport of membrane-bounded vesicles. For example, mutations In the myosin V gene In yeast disrupt protein secretion and lead to an accumulation of vesicles In the c rt oplasm. Vertebrate brain tissue Is rich In myosin V, which Is concentrated on Golgi stacks. This association with membranes Is consistent with the effects of myosin V mutations In mice. Such mutations are associated with defects In synaptic transmission and eventually cause death from seizures. Myosin VI also Is Implicated In membrane trafficking of vesicles. 

The mechanism of this transport is presently unknown, but the results are consistent with a soluble carrier mechanism such as PC transfer protein, or transport at zones of apposition between membranes that facilitate rapid intermembrane transfer. Work by Pichler and colleagues has identified a subfraction of the ER that associates closely with the plasma membrane in yeast (H. Pichler, 2001). Future studies examining the effects of agents or mutations that disrupt these intracellular membrane associations will be critical for determining their role in lipid traffic. 

It is used principally in the treatment of tinea pedis, tinea cruris, tinea corporis, tinea manuum, and tinea versicolor. Haloprogin s mechanisms of action in yeast cells are thought to be inhibition of respiration and disruption of yeast cell membranes. Its mechanism of action in dermatophytes is unknown. 

---