fusionspore

Fusionspore is a transient, regulated channel formed at the site of membrane fusion between two lipid bilayers, typically a vesicle and its target membrane. It represents the initial, narrow conduit that permits limited exchange between compartments before the membranes fully merge. In many descriptions, the fusionspore precedes the fully dilated fusion pore and can reseal if the fusion process is aborted.

Formation is driven by fusion machinery that pulls membranes together, including protein complexes analogous to SNAREs, as well as lipid rearrangements and curvature stresses. The pore is stabilized by accessory factors and can be gated by calcium or other signaling molecules. The diameter of a fusionspore is small, often only a few nanometers, and it may permit ion flux and small molecule passage without immediate cargo release.

Biological relevance and observations. The concept has been discussed in studies of regulated exocytosis, synaptic transmission, and some virus-cell fusion models where a narrow, controllable connection influences release timing. Experimental evidence comes from high-resolution imaging and electrophysiological measurements showing transient, sub-pore conductance events corresponding to fusionspore states. The exact kinetics can affect release rates and selectivity.

Research status and terminology. The term fusionspore emphasizes the early stage of membrane fusion and its regulatory dimension, distinct from the later, larger fusion pore. It remains a topic of active investigation, with ongoing work using simulations, cryo-electron microscopy, and fusion assays to map its formation, lifespan, and transitions to full fusion.