N-ethylmaleimide sensitive fusion protein

N-ethylmaleimide-sensitive factor, also known as NSF or N-ethylmaleimide sensitive fusion proteins, is a human gene. It is a trimeric ATPase involved in membrane fusion. NSF is ubiquitously found in the cytoplasm of eukaryotic cells. It is a central component of the cellular machinery in the transfer of membrane vesicles from one membrane compartment to another. During this process, SNARE proteins on two joining membranes (usually a vesicle and a target membrane such as the plasma membrane) form a tight complex. This aids fusion of the vesicle with the target membrane. The role of NSF is to undo these SNARE complexes once membrane fusion has occurred, using the hydrolysis of ATP as an energy source. The dissociated SNAREs can then be recycled for reuse in further rounds of membrane fusion.

SNARE hypothesis
Because neuronal function depends on the release of neurotransmitters at a synapse — a process in which synaptic vesicles fuse with the presynaptic membrane — NSF is a key synaptic component. Thus, conditional temperature-sensitive mutations in the Drosophila gene for NSF lead to a comatose behaviour at the restrictive temperature (and hence the gene is called comatose), presumably because neuronal functions are blocked. In Dictyostelium amoebae, similar mutations lead to a cessation of cell movement at the restrictive temperature, indicating a role for intracellular membrane transport in migration. Another neuronal role for NSF is indicated by its direct binding to the GluR2 subunit of AMPA type glutamate receptors (which detect the neurotransmitter glutamate). This gives NSF a putative role in delivery and expression of AMPA receptors at the synapse.

NSF was discovered by James Rothman and colleagues in 1979 whilst at Stanford University; they identified NSF after observing that a cytoplasmic factor, required for membrane fusions, was inactivated by treatment with N-ethylmaleimide. This assay enabled them to purify NSF.