Membrane Proteins

Peripheral Membrane proteins

proteins that are relatively loosely attached to the membrane and can be dissociated under mild conditions

Integral Membrane Proteins

proteins that interact extensively with lipid hydrocarbon chains, most span the bilayer, can be extracted from the membrane only with detergents or other agents that disrupt the membrane

Beta-barrel integral proteins

antiparallel beta sheets curl to form a cylinder, acts as a pore or channel; outside surface is nonpolar and inside surface that lines pore is hydrophilic

Porins

membrane proteins in outer membrane of gram-negative bacteria and mitochondira/chloroplasts, forms channels to allow entry of small solutes; type of beta-barrel integral protein

FepA

porin responsible for iron uptake

Maltoporin

porin that allows transport of maltose

OmpLA

porin that allows transport of phospholipase

alpha-helical membrane proteins

most integral membrane proteins, have alpha helixes that traverse the membrane

glycophorin A

protein in erythrocyte membrane that contains a single membrane spanning alpha helix

bacteriorhodopsin

protein in helicobacterium halobium that acts as a light-driven protein pump, contains 7 transmembrane alpha helices

G-Protein Coupled Receptors

integral proteins that transverse the membrane seven times

Hydropathy Plots

allows for identification of segments in a polypeptide chain with overall hydrophobicity; scan sequences over a window of about 20 amino acid residues to ID potential transmembrane alpha helices

Lipid Anchored Proteins

Proteins are associated to membranes via a covalent link to a lipid, this is a reversible attachment

thioester linked fatty acid

covalent linkage of a fatty acid via an ester bond to cysteine, serine, or threonine

Amide-linked myristoyl

mystiric acid is linked via amide bond to N-terminal glycine residue

Prenyl Anchors

anchors derived from isoprene (C5 compound)— prenyl anchor associates with membrane and binds C-terminal CAAX sequence of a protein

amide linked glycosyl phosphatidylinositol

phosphatidylinositol glycosdically linked to a linear tetra-saccharide linked with a phosphodiester bond to phosphoetholamine which is amide linked to C-terminal carboxyl group

GPI

glycosylated derivatives of phosphatidylinositol