About this Research Topic
Lipid biomembranes act as selectively permeable barriers that define the boundaries of cells and their internal compartments. Biological membranes can segregate into dynamic nano- and micro-domains of complex, albeit specific, lipid and protein composition resulting in largely varying local membrane order and dynamics. In addition to lateral segregation, all biological membranes expose an asymmetry in composition between the inner cytosolic and the outer membrane leaflets that is both actively maintained (e.g. by flippases or asymmetric biosysnthesis and degradation of lipids) and partly passively underpinned by membrane curvature and specific protein-lipid interactions. Both the membrane asymmetry and the lateral partitioning into so-called ordered and disordered membrane domains play an important role for the sorting and trafficking of membrane constituents to the cell plasma membrane, enable the proximity of cascading molecules for efficient signaling, provide a directionality for cell growth, sensing, and migration, or affect endocytosis.
A field in which most, if not all, of these cell functions play a critical role is immunology. Innate immune cells such as macrophages or neutrophils have to operate under extreme conditions such as oxidative stress, high salt and high sheer stress. When immune cells leave the blood they have to adopt their cytoskeleton and plasma membrane to attach to blood vessels and leave the vasculature without perturbing blood vessel integrity. Moreover, cell signalling, endocytosis and exocytosis of highly toxic substances have to be regulated very tightly to prevent systemic damage to healthy cells. Thus, understanding cell membrane dynamics and nano-/microdomain organization in immune cells is of critical importance to understand and regulate immune cell function.
The sizes and dynamics of coexisting membrane domains is determined by the membrane composition and environmental conditions such as temperature and pressure. Cells have established sophisticated mechanisms to regulate their membrane compositions and to sense specific physicochemical membrane properties to ultimately control the dynamic coexistance of different membrane domains under physiological conditions.
Despite its seemingly important role for cell life, research on the mode of action of membrane heterogeneities is scarce thus severely limiting our understanding of biology at the boundaries of life. The aim of this topical issue is to decipher the role of heterogeneities in biomembranes, ranging from physical mechanisms for lateral membrane domain formation and dynamics, the structure and dynamics of domain interfaces, the registration of inner and outer membrane leaflets in domain formation, the regulation of the composition of biomembrane domains, and in particular the functional integration of the different membrane phases into cellular physiology and immune processes. The central question is: how does the cell make use of membrane nano- and microdomains and what are the physical mechanisms governing lateral membrane segregation and interleaflet coupling?
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