New insight in calcium-induced membrane fusion
A new study published on 18 September 2015 in Nature Communications provides new insight in the mechanism of cellular secretion. The results emerge from a collaborative study by the groups of Sander Groffen (Molecular mechanisms of secretion) and Gijs Wuite (Physics of Living Systems).
For each secretory event, the membrane of a secretory vesicle needs to fuse with the membrane at the cell surface. The researchers established an advanced optical technique called ‘optical tweezers’ to study these membrane fusion events as they happen in real-time. Instead of using living systems, they used synthetic membranes and proteins to rebuild a minimal part of the secretion machinery. The investigators observed that the Ca2+ sensor protein Doc2b enhanced the probability of secretion by stabilizing an intermediate state of the membrane fusion reaction, termed hemifusion. Because other important proteins of the secretory machinery were excluded in their experiments, the authors conclude that after activation by Ca2+ ions, Doc2b directly acts on specific phospholipids in the membrane.
Secretory processes are fundamental to a broad spectrum of biological processes such as neurotransmission in the brain and the release of hormones into the blood. The novel technique and the new insights are thus relevant to a wide field of future research.