section 2 脂类与生物膜PPT.ppt

Integrins (整合素）：consist of and transmembrane polypeptides; their extracellular domains combine to form binding sites for divalent metal ions and proteins of the extracellular matrix (such as collagen and fibronectin) or for specific surface proteins of other cells. Cadherin（钙粘着蛋白）：has four extracellular Ca2+-binding domains, the most distal of which contains the site that binds to cadherin on another cell surface. N-CAM ：(neuronal cell adhesion molecule) is one of a family of immunoglobulin-like proteins that mediate Ca2+- independent interactions with surface proteins of nearby cells. Selectins（选凝素）： bind tightly to carbohydrate moieties in neighboring cells; this binding is Ca2+-dependent. The fusion of two membranes is central to a variety of cellular processes involving both organelles and the plasma membrane. A remarkable feature of the biological membrane is its ability to undergo fusion with another membrane without losing its continuity. 2 Membrane Fusion  (膜融合) Is Central  to Many Biological Processes 2.1 Specific fusion of two membranes requires that ： (1) they recognize each other; (2) their surfaces become closely apposed, which requires the removal of water molecules normally associated with the polar head groups of lipids; (3) their bilayer structures become locally disrupted, resulting in fusion of the outer leaflet of each membrane (hemifusion); (4) their bilayers fuse to form a single continuous bilayer. Receptor mediated endocytosis, or regulated secretion, also requires that (5) the fusion process is triggered at the appropriate time or in response to a specific signal. Integral proteins called fusion proteins mediate these events, bringing about specific recognition and a transient local distortion of the bilayer structure that favors membrane fusion. 2.2 Two cases of membrane fusion are especially well studied: the entry into a host cell of an enveloped virus such as influenza virus the release of neurotransmit