(388f) Tunable Nucleation Time of Functional Sphingomyelinase-Lipid Complex

Cell membranes are composed of various types of lipids and proteins. Phase separation, or called lipid membrane heterogeneity, exists in this multi-component system. The phase dynamics has been suggested to influence many cellular processes. We report that a type of peripheral membrane protein, sphingomyelinase (SMase), can form a functional complex with its lipid substrate and product on the lipid membrane, and has a tunable formation time based on classical nucleation theory. The enzyme's hydrolysis rate is found to significantly increase after the complex is formed. We found that the nucleation rate of the complex can be tuned or predicted by the supersaturation of the enzyme, the lipid substrate and the lipid product. The complex nucleation is found to be influenced by the component concentrations in the fluid phase, where the complex nucleates, suggesting that the property in the interested phase instead of the apparent property in the entire system is important in the phase segregated lipid membrane. More generally, our finding suggests that nucleation could serve as a time lag control mechanism in this enzymatic system, while many of the time lags in biology are controlled by diffusion time or reaction kinetic delay. Ways to reduce nucleation energy barrier could be used to shorten the aggregation time lag and vice versa.