1. Membrane Proteins BSCI 420,421Lecture 16Oct 8,9, 2002 “And you shall know the truth, and the truth shall set you free.” -Jesus of Nazareth

2. MEMBRANE PROTEINS are associated with the lipid bilayer In several different ways: Most are transmembrane proteins: 1.Single pass  helix, 2. multiple  helices  barrels. 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).

3. 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.

4. A single pass transmembrane protein e,g, glycophorin on RBCs Or receptor tyrosine kinases

5. Beta barrels-beta sheets wrapped around a water filled pore. (hydrophobic AAs out, hydrophilic Aas in) 1.A Receptor 2.A lipase enzyme 3.A Channel 4.An iron transporter

7. Dissolving, purifying, and reconstituting membrane proteins to test their f(x).

8. SEM of human RBCs - Easiest place to isolate PM Because no internal membranes

9. Prep. Of RBC ghostsSDS-PAGE

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

12. Three domains in the plasma membrane of a spermatozoan These domains are bounded By rows of proteins, seen as particles in freeze fracture TEM. (Held in place by underlying strictures)