Macromolecular crowding and inhibition of ice crystallization.

摘要

Cell cytoplasm is a crowded environment where a large fraction of volume is occupied by other macromolecules. Crowding effect on protein-protein association kinetics is investigated using computational and theoretical approaches of a hard sphere model. The effect of orientation-dependent protein reactivity is investigated in terms of a reaction probability upon collision. It is shown that the associations of two proteins with large reactivity slow down with crowding due to the reduced diffusion while those with small reactivity are accelerated due to the increased re-encounter probability between a unreacted pair of proteins. An application is made to membrane protrusion by actin filament elongation and it is shown that the velocity of membrane protrusion increases due to the increased local concentration of actin monomers near actin filament tips below membranes.;The inhibition of ice crystallization is investigated by molecular dynamics simulations with atomistic models. New insights into melting of ice by salts are provided in terms of water exchange between ice and liquid water. It occurs in two stages: association of water molecules with ice surface is reduced and then dissociation from ice surface is enhanced, resulting in the decrease of the number of water molecules in ice. When the peptides abundant in collagen hydrolysates are placed in the vicinity of ice/water interface, the growth of ice crystal is significantly retarded. The presence of a specific residue, proline, confers a better retardation of ice growth. This study suggests that short peptides readily available can be utilized to inhibit the ice growth when engineered with specific residues.;The effect of sodium chloride on diffusivity of water at subzero temperatures is studied. The dependence of the diffusion coefficient of water on salt concentration is qualitatively different at temperatures above and below zero, and the transition of sodium chloride from a structure-maker at room temperature to a structure-breaker at subzero temperatures is observed.