Homeoviscous Adaptation and the Regulation of Membrane Lipids

Biological membranes are complex and dynamic assemblies of lipids and proteins. Poikilothermic organisms including bacteria, fungi, reptiles, and fish do not control their body temperature and must adapt their membrane lipid composition in order to maintain membrane fluidity in the cold. This adaptive response was termed homeoviscous adaptation and has been frequently studied with a specific focus on the acyl chain composition of membrane lipids. Massspectrometry-based lipidomics can nowadays provide more comprehensive insights into the complexity of lipid remodeling during adaptive responses. Eukaryotic cells compartmentalize biochemical processes in organelles with characteristic surface properties, and the lipid composition of organelle membranes must be tightly controlled in order to maintain organelle function and identity during adaptive responses. Some highly differentiated cells such as neurons maintain unique lipid compositions with specific physicochemical properties. To date little is known about the sensory mechanisms regulating the acyl chain profile in such specialized cells or during adaptive responses. Here we summarize our current understanding of lipid metabolic networks with a specific focus on the role of physicochemical membrane properties for the regulation of the acyl chain profile during homeoviscous adaptation. By comparing the mechanisms of the bacterial membrane sensors with the prototypical eukaryotic lipid packing sensor Mga2 fromSaccharomyces cerevisiae,we identify common operational principles that might guide our search for novel membrane sensors in different organelles, organisms, and highly specialized cells.