Evolutionary conservation of the membrane fusion machine

Recent structural studies of proteins mediating membrane fusion reveal intr iguing similarities between diverse viral and mammalian systems. Particular ly striking is the close similarity between the transmembrane envelope glyc oproteins from the retrovirus HTLV-1 and the filovirus Ebola. These similar ities suggest similar mechanisms of membrane fusion. The model that fits mo st currently available data suggests fusion activation in viral systems is driven by a symmetrical conformational change triggered by an activation ev ent such as receptor binding or a pH change. The mammalian vesicle fusion m ediated by the SNARE protein complex most likely occurs by a similar mechan ism but without symmetry constraints.