Cell Biology BIOL 266

Membrane proteins

Types of Membrane proteins

Integral, Lipid-anchored, Peripheral

Integral Proteins

embedded fully/partially in membrane

monotopic

embedded in membrane

Transmembrane

span lipid bilayer, ends stick out

amphipathic

patially polar (ends), partially non polar(span)

Lipid anchored proteins

linked to a lipid embedded in membrane

Types of Lipid Anchored proteins

GPI-anchored: anchored to a glychosylated phosphotidylinositiol

Fatty acid: anchored to a fatty acid

Isopropernylation: anchored to many isporene groups (farsenyl, geranyl geranyl)

Peripheral Proteins

associated with membrane by electrostatic bonds. Can be removed using a high concentration of salt or pH (on outside of membrane associate with charged polar head groups)

amphipathic helix

many alpha helicies (H on O at Ri and H at N at Ri+4) from a multipass protein form a hydrophilic pore to allow transport of large polar molecules across membrane

alpha helicies

1 turn=o.54nm=3.6 residues

amphipathic B-barrels

B sheets create a amphipathic B barrel channels to allow transport of large polar/charged molecules

membrane domain

cluster of proteins at specific point (if protein movement is restricted)

Can be restricted by:

interaction b/w proteins (aggregation w/ similar prot or attraction w/ extracellular)

intearction b/w prot and cytoskeleton

interaction b/w prot on two diff cell membranes

lipid rafts

membrane domain w? cholestreol, GPI anchore, gylcosphingolipids, makes rigid thick structure with low diffusion