Mechanism of intercellular communication

Chemical messengers (like - hormones, neurotransmitters, neuropeptides, cytokines etc.) are entrapped inside the membrane enclosed vesicles within the cell. These vesicles fuse with the plasma membrane in spatiotemporally coordinated manner, to release their content outside the cell, thus establishing the intercellular communication. This process is called exocytosis. Much of the functional repertoire of exocytosis depends on the fusion pore, the first aqueous connection that forms between the lumen of secretory vesicles and the cell exterior (for further reading: Lindau M. & Almers W., Curr Opin Cell Biol. 1995,7(4):509-17; Jackson M.B. & Colleagues, J. Gen. Physiol. 2017,149(3):301-322). These are nm-scale transient structures, lasting only milliseconds before they either close, or dilate such that the vesicle membrane collapses into the plasmalemma. The soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNAREs) are proteins that catalyze the formation of fusion pore and serve as the minimal machinery required for vesicle fusion (for further reading: Sudhof T. & Rothman J., Science 2009, 323(5913): 474-477). A number of groundbreaking studies have improved our present understanding of the SNARE mediated vesicle fusion. Still we have very limited knowledge about the structure-function relationship of the fusion pores and how accessory proteins directly or indirectly modulate the pore properties. This information is crucial to understand, how, chemical messengers are secreted constitutively and regulated manner. In depth understanding of which will, in turn, help to therapeutically modulate the cellular secretion under various pathological conditions.

In our lab, we investigate:

• Whether fusion pore acts as a pathway for passive diffusion of chemical messengers or it is an active valve that regulates vesicular secretion.

• Structure-function relation of fusion pores. How do the accessory factors regulate the fusion pores assembly / disassembly?

• What is the molecular basis of abnormal vesicular secretion?

Our lab utilizes a range of steady-state and time resolved ensemble measurements, to address the questions, which are otherwise impossible to understand within the cell. Additionally, we use lipid scaffold protein (e.g. apolipoprotein variants, saposins etc.) based planar bilayer electrophysiology technique, to study the open and close dynamics of a single recombinant fusion pore, in micro-second time resolution. We perform experiments using PC12 cells and cultured neurons, to further justify our in vitro observation.