In vivo phase and dynamical behavior of intracellular lipid droplets

Lipid Droplets are complex cellular organelles generated by all cells in response to elevated fatty acid levels. They represent a core full of triacylglycerols enclosed by a phospholipid monolayer with embedded associated proteins. LD is a source of lipids for metabolism and membrane synthesis. However, knowledge of the state and internal molecular motions of LD in its natural environment, whole cell, is lacking. Our model system is a microorganism Cryptococcus curvatus ATCC20509. The cells of this oleaginous yeast are capable of assimilating glucose and accumulate 60% of LDs. We applied Quasi-Elastic Neutron Scattering to uncover intrinsic characteristics of LDs located in living cells. It has been shown that this technique successfully probes individual components in a complex environment. Elastic incoherent neutron scattering scan over temperature range detects a phase transition in the droplets at 297 K. This change from the gel to fluid phase is similar to that observed for model lipid bilayer membranes [Sharma et al, JPCB 2016]. Such phase behavior of LDs manifests itself in a change in the long-range translational lipid dynamics. Besides, analysis of QENS signal originated specifically from droplets reveals the localized lipid dynamic component.