Cyclic 3',5'-AMP causes ADAM1/ADAM2 to rapidly diffuse within the plasma membrane of guinea pig sperm.

Because sperm cannot synthesize new proteins as they journey to the egg, they use multiple mechanisms to modify the activity of existing proteins, including changes in the diffusion coefficient of some membrane proteins. Previously, we showed that during capacitation the guinea pig heterodimeric membrane protein ADAM1/ADAM2 (fertilin) transforms from a stationary state to one of rapid diffusion within the lipid bilayer. The cause for this biophysical change, however, was unknown.

Membrane hemifusion is a stable intermediate of exocytosis.

Membrane fusion during exocytosis requires that two initially distinct bilayers pass through a hemifused intermediate in which the proximal monolayers are shared. Passage through this intermediate is an essential step in the process of secretion, but is difficult to observe directly in vivo. Here we study membrane fusion in the sea urchin egg, in which thousands of homogeneous cortical granules are associated with the plasma membrane prior to fertilization.

FUS1 regulates the opening and expansion of fusion pores between mating yeast.

Mating yeast cells provide a genetically accessible system for the study of cell fusion. The dynamics of fusion pores between yeast cells were analyzed by following the exchange of fluorescent markers between fusion partners. Upon plasma membrane fusion, cytoplasmic GFP and DsRed diffuse between cells at rates proportional to the size of the fusion pore.

Lipids in the inner membrane of dormant spores of Bacillus species are largely immobile.

Bacterial spores of various Bacillus species are impermeable or exhibit low permeability to many compounds that readily penetrate germinated spores, including methylamine. We now show that a lipid probe in the inner membrane of dormant spores of Bacillus megaterium and Bacillus subtilis is largely immobile, as measured by fluorescence redistribution after photobleaching, but becomes free to diffuse laterally upon spore germination. The lipid immobility in and the slow permeation of methylamine through the inner membrane of dormant spores may be due to a significant (1.

A soluble protein is immobile in dormant spores of Bacillus subtilis but is mobile in germinated spores: implications for spore dormancy.

Fluorescence redistribution after photobleaching has been used to show that a cytoplasmic GFP fusion is immobile in dormant spores of Bacillus subtilis but becomes freely mobile in germinated spores in which cytoplasmic water content has increased approximately 2-fold. The GFP immobility in dormant spores is not due to the high levels of dipicolinic acid in the spore cytoplasm, because GFP was also immobile in germinated cwlD spores that had excreted their dipicolinic acid but where cytoplasmic water content had only increased to a level similar to that in dormant spores of several other Bacillus species. The immobility of a normally mobile protein in dormant wild-type spores and germinated cwlD spores is consistent with the lack of metabolism and enzymatic activity in these spores and suggests that protein immobility, presumably due to low water content, is a major reason for the metabolic dormancy of spores of Bacillus species.