Model Systems, Lipid Rafts, and Cell Membranes

Abstract

Views of how cell membranes are organized are presently changing. The lipid bilayer that constitutes these membranes is no longer understood to be a homogeneous fluid. Instead, lipid assemblies, termed rafts, have been introduced to provide fluid platforms that segregate membrane components and dynamically compartmentalize membranes. These assemblies are thought to be composed mainly of sphingolipids and cholesterol in the outer leaflet, somehow connected to domains of unknown composition in the inner leaflet. Specific classes of proteins are associated with the rafts. This review critically analyzes what is known of phase behavior and liquid-liquid immiscibility in model systems and compares these data with what is known of domain formation in cell membranes.

Increased localization of APP‐C99 in mitochondria‐associated ER membranes causes mitochondrial dysfunction in Alzheimer disease

“…Given that MAM is a lipid raft (Area‐Gomez et al , 2012), we speculated that C99 could have a role in MAM activity and in ER–mitochondrial connectivity through changes in MAM lipid composition (Simons & Vaz, 2004). We therefore performed lipidomic analyses of total homogenates, mitochondrial fractions, and isolated MAM from PS‐DKO MEFs and controls.…”

Lipid rafts: contentious only from simplistic standpoints

“…The classic lipid-raft hypothesis postulates that rafts pre-exist in the plasma membrane 1,3 . Proteins with lipid anchors or transmembrane domains that are able to partition into an L o environment are sequestered or concentrated in these rafts.…”

“…The basic concept is that lipid rafts can facilitate selective protein-protein interactions by selectively excluding or including proteins. This lipid-based sorting mechanism has been widely implicated in the assembly of transient signalling platforms and more permanent structures such as the immunological synapse, as well as in the sorting of proteins for entry into specific exocytic and endocytic trafficking pathways [1][2][3] . Despite the undoubted theoretical utility of lipid rafts to many cell biological processes, the basic hypothesis that stable lipid rafts exist at all in biological membranes is under intense scrutiny 4,5 .…”

Coordination and transport of alkali metal cations through phospholipid bilayer membranes by hydraphile channels

“…They are generally found in the plasma membrane outer leaflet. Taken together, the numerous membrane components [10] pose a formidable barrier through which only gases and small, uncharged molecules can pass [11]. Phospholipid bilayers are impermeable to large molecules, very polar molecules, and ions.…”