Plasma membranes are asymmetric in lipid unsaturation, packing and protein shape.

A fundamental feature of cellular plasma membranes (PMs) is an asymmetric lipid distribution between the bilayer leaflets. However, neither the detailed, comprehensive compositions of individual PM leaflets nor how these contribute to structural membrane asymmetries have been defined. We report the distinct lipidomes and biophysical properties of both monolayers in living mammalian PMs. Phospholipid unsaturation is dramatically asymmetric, with the cytoplasmic leaflet being approximately twofold more unsaturated than the exoplasmic leaflet. Atomistic simulations and spectroscopy of leaflet-selective fluorescent probes reveal that the outer PM leaflet is more packed and less diffusive than the inner leaflet, with this biophysical asymmetry maintained in the endocytic system. The structural asymmetry of the PM is reflected in the asymmetric structures of protein transmembrane domains. These structural asymmetries are conserved throughout Eukaryota, suggesting fundamental cellular design principles.

Author Correction: Plasma membranes are asymmetric in lipid unsaturation, packing and protein shape.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The ageing of the population--a time for action. The role of public health.

The past two decades have witnessed the growth of the over-60, "elderly" population both in numbers and life expectancy. Similarly, there has been a shift in overall morbidity from acute to chronic causes and associated lifestyle factors. The increasing elderly population provides health care planners with new challenges at a time of decreasing resources. The public health approach, which equally stresses the responsibility of the individual, the family, the community and health care providers, is suggested as the starting point for addressing the issue.