BIOL 266 : Unit 4

Includes TOP Hat of unit 4 and some SmartWork

% of proteins associated with membrane?

30%

% of therapeutic targets are integral membrane proteins?

60%

Why would therapeutic targets/molecules bind to plasma membranes?

To help diffuse polar molecules

% of membrane weight that is contributed by proteins?

50%

_______ are much larger than _____

Proteins, lipids

____ lipid molecules per membrane proteins

~100

What are proteins responsible for?

Carrying out specific membrane functions

What are the three distinct classes of membrane proteins ?

Integral membrane proteins / Lipid anchored proteins / Peripheral proteins

2 Characteristics of Integral membrane proteins

Pass through the lipid bilayer. Are amphipathic.

Monotopic protein

Embedded in the membrane but does not emerge from both sides.

Orientation of odd number integral protein membrane spanning domain?

In-out orientation

Orientation of even number integral protein membrane spanning domain?

In-in or out-out orientation

Lipid-anchored proteins

The protein is linked to a lipid which embeds in the membrane.

Three main types of lipid-anchored proteins

GPI-anchored / fatty acid anchored / Isoprenylation anchor

GPI-anchored

The protein is covalently attached to glycosylated phosphatidylinositol.

If GPI-anchored are mainly found on the external side of the plasma membrane, where was it originally synthesized ?

In the lumenal side of the ER

Fatty acid anchored

Protein is linked to a fatty acid

Isoprenylation anchor

The protein can be attached to multiple isoprene (5 carbon) groups (isoprenylated).

Peripheral proteins

Attached to the membrane by weak electrostatic bonds and are easily solubilized. Associate membrane surface by non-covalent bonds.

Peripheral membrane proteins can associate either with ___________________

Integral membrane proteins or with the charged or polar head groups of lipids.

How to remove peripheral membrane proteins from the membrane?

Using agents that disrupt electrostatic interactions.

Agents that disrupt electrostatic interactions

Extreme pH/solutions with high concentrations of salt.

4 Functions of membrane proteins

Transport molecules across the membrane / anchor proteins on either face to the membrane / receptors that detect chemical signals and relays them / enzymes to catalyze reactions .

Proteins cross the membrane as an ____

alpha-helix.

Proline residues

Are not found in an a-helix.

The hydrogen of one peptide bond forms a hydrogen bond with the oxygen of a peptide bond ________.

Four residues away

How many hydrophobic amino acids are needed to get through the hydrophobic layer of the lipid bilayer ? Lipid bilayer = 5 nm

Hydrophobic part = 2.5 nm

α-helix = 0.54 nm

2.5 / 0.54 = 4.63 → “ How much of the helix fits in the hydrophobic bilayer”

4.63 x 3.6 = 17

β-sheets Can form hydrogen bonds with residues that are_____.

far-removed

Parallel β-sheets.

Antiparallel β-sheets.

Which phospholipase would you expect to be involved in signaling?

PLC

Which of the following could be part of a transmembrane ∝-helix that crosses the bilayer one time?

CHOICES FOR THE AMINO ACID IMPAIRED

A. -Asp-Gly-Val-Leu-Arg-Ser-Ile-Ala-Glu-Thr-

B. -Ile-Leu-Ala-Pro-Gly-Gly-Leu-Pro-Val-Phe-

C. -Ile-Leu-Val-Ala-Leu-Leu-Ala-Phe-Ala-Val-

D. All three could be part of such an ∝-helix

C

Integral proteins:

Peripheral proteins:

If a patch of animal cell membrane has about 10 μm in area, there will be more _____ than _____.

Lipids, Proteins

lipids are much smaller than proteins, so a cell membrane typically contains 50 times more _________________.

lipid molecules than protein molecule

Treatment with high salt would release ___________

peripheral proteins from the bilayer.

Treatment with phospholipase C would cleave the phospholipid anchor of a ______________

GPI-anchored protein.

The most commonly used reagents for solubilization of transmembrane proteins are _________

detergents.

Detergents are _____ and ______ molecules.

small, amphipathic

Detergent molecules are shaped more like ______

cones.

Detergents have only a single _____ _____

hydrophobic tail.

Lipids with two hydrophobic tails assume a more _____ _____

cylindrical shape.

Cellular Adhesion Molecules (CAMs) mediate _____ _____ _____.

binding between cells

Homophilic molecules

Bind to the same molecule on a different cell.

heterophilic molecules

Bind to a different molecule on a different cell

Lipid raft

Domain on the membrane that has a high concentration of the specific lipids.

You can use ____ on protein to determine recovery rate of the protein.

FRAP