Microdomain Organization of the Plasma Membrane in Keratinocytes

Abstract

Plasma membrane of the keratinocyte is organized in a domain structure comprising the nanoscale areas of the lipid in the liquid ordered state (comparable to lipid rafts) surrounded by the liquid-disordered lipid fraction. In this review we summarize the current state of knowledge on the microdomain organization of the keratinocytes plasma membrane. Application of the fluorescent derivative of cholera toxin B1 subunit cross-links these domains into larger, nanometerscale units in which molecular movement of proteins and lipids is retarded. Microdomain cross-linking is particularly effective in the basal portion of the cell within the focal junctions. Thus, junctional structures can behave as molecular sieves in which the density of microdomains is increased. Since lipid rafts play a role in transmembrane signal transduction (see other articles in this supplementum) these finding can explain the compartmentalization of signaling processes in the membrane. Research has also revealed how the microdomain organization of keratinocytes plasma membrane determines membrane curvature and regulates the formation of exocytotic vesicles and filopodia-like structures. Coalescence of a large number of microdomains into larger subunits can bend the membrane by the force generated on he lipid ordered/lipid disordered interphase. Microdomain composition of the membrane can also add another dimension to the explanation of skin pathology such as epidermal hyperplasia, apoptosis, cell-cell adhesion and disorders of cornification.