Non-linear solitary sound waves in lipid membranes and their possible role in biological signaling.
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Abstract
Biological macromolecules self-assemble under entropic forces to form a
dynamic 20 interfacial medium where the elastic properties arise from the curvature of
the entropic potential of the interface. Elastic interfaces should be capable of propagating localized perturbations analogous to sound waves. However, (1) the existence and (2) the possible role of such waves in affecting biological functions remain unexplored. Both these aspects of "sound' as a signaling mechanism in biology are explored
experimentally on mixed monolayers of lipids-fluorophores-proteins at the air/water
interface as a model biological interface.
This study shows - for the first time - that the nonlinear susceptibility near a
thermodynamic transition in a lipid monolayer results in nonlinear solitary sound waves
that are of 'all or none ' nature. The state dependence of the nonlinear propagation is
characterized by studying the velocity-amplitude relationship and results on distance
dependence, effect of geometry and collision of solitary waves are presented. Given that
the lipid bilayers and real biological membranes have such nonlinearities in their
susceptibility diagrams, similar solitary phenomenon should be expected in biological
membranes. In fact the observed characteristics of solitary sound waves such as, their all
or none nature, a biphasic pulse shape with a long tail and optp-mechano-electro-thermal
coupling etc. are strikingly similar to the phenomenon of nerve pulse propagation as
observed in single nerve fibers.
Finally given the strong correlation between the activity of membrane bound
enzymes and the susceptibility and the fact that the later varies within a single solitary
pulse, a new thermodynamic basis for biological signaling is proposed. The state of the
interface controls both the nature of sound propagation and its impact on incorporated
enzymes and proteins. The proof of concept is demonstrated for acetylcholine esterase
embedded in a lipid monolayer, where the enzyme is spatiotemporally "knocked out" by a
propagating sound wave.
Description
Thesis (Ph. D.)--Boston University