Chapter 8 - From Lipid Bilayers to Lipid Rafts

Abstract

By 1935 basic elements were in place to propose a realistic membrane model. This was accomplished by Danielli-Davson in their ‘Pauci-Molecular Model’, based on a lipid bilayer that had proteins uncomfortably attached in the form of a protein - lipid - protein sandwich. A slight improvement to this model was proposed by Robertson in his 1957 ‘Unit Membrane Model’. His model was based on electron micrographs, the first direct observations of membrane structure, and featured ‘railroad tracks’. In the 1960s Benson (for the photosynthetic thylakoid) and Green (for the mitochondrial inner membrane) proposed lipid bilayer-free models called ‘Lipoprotein Subunit Models’. These early models did not appreciate membrane asymmetry or dynamics. In 1972 Singer-Nicholson proposed their ‘Fluid Mosaic Model’ that retained the lipid bilayer, but accounted for previous model shortcomings, recognizing membrane fluidity and lateral mobility. An addition to this model was provided by Kai Simon’s 1997 ‘Lipid Raft Model’ that proposed sphingolipid- and cholesterol-rich, liquid ordered, signaling microdomains.