Membrane Proteins

BSCI 420,421 Lecture 16 Oct 8,9, 2002

“And you shall know the truth, and the truth shall set you free.”

-Jesus of Nazareth

MEMBRANE PROTEINS are associated with the lipid bilayerIn several different ways: Most are transmembrane proteins: 1. Single pass helix, 2. multiplehelicesbarrels.4. Others are anchored in one layer by a helix.These are all Integral membrane proteins (can be removed only by dissolving the membrane with a solvent or detergent).

5&6 are integral proteins bound by lipid anchors in the bilayer,Either a prenyl chain or a phospholipid.7&8 are peripheral membrane proteins: These associate with Integral proteins by protein-protein interactions & can be removed by high salt rinses.

A single pass transmembrane protein e,g, glycophorin on RBCsOr receptor tyrosine kinases

Beta barrels-beta sheets wrapped around a water filled pore.

(hydrophobic AAs out, hydrophilic Aas in) 1. A Receptor2. A lipase enzyme3. A Channel4. An iron transporter

Dissolving, purifying, and reconstituting membrane proteins totest their f(x).

SEM of human RBCs - Easiest place to isolate PMBecause no internal membranes

Prep. Of RBC ghosts SDS-PAGE

Membrane proteins are delivered to specific membrane compartments or domains and kept there by junctionsor domain boundaries. E.g. in epithelia, tight jxs separateapical from basolateral proteins.

Three domains in the plasma membrane of a spermatozoan

These domains are boundedBy rows of proteins, seen asparticles in freeze fracture TEM. (Held in place by underlying strictures)