Question

Membrane Protein Census

(a) Table 1 of Mitra et al. (2004) reports the mass ratio of proteins and phospholipids in the membranes of various cells and organelles. Use the asserted 2.0mg of protein for every 1.0mg of phospholipid in the E. coli membrane to compute the areal density of membrane proteins and their mean spacing. Make a corresponding estimate for the membrane of the endoplasmic reticulum using the fact that the mass ratio in this case is 2.6. Explain all of you assumptions in making the estimate.

(b) Dupuy and Engelman (2008) report that the area fraction associated with membrane proteins in the red blood cell membrane is roughly 23%, while the lipids themselves take up roughly 77% of the membrane area. Use these numbers to estimate the number of membrane proteins in the red blood cell membrane and their mean spacing. Explain all theassumptions you make in constructing the estimate.

Answer 1

Solution -

(a) assumptions making the estimate for the reports are -

1. The proteins are the larger as compare to the phospholipids.

2. The The E.coil membrane having the 2.0mg protein for every 1.0mg phospholipid.

3. The protein and phospholipid using this ratio for proceeding the areal density of membrane proteins and their mean spacing.

4. They also assume that because some cellular membrane are not determine by the phospholipids but by their protein. Some membrane associated protein transport by ions and other molecules.

(b) Assumptions are

1. The transmembrane proteins are surrounded by phospholipids. 2. These phospholipids are perturbed by their presence , the occupancy by protein of more than 20% of the RBC plasma membrane. 3.The pure lipid bilayers do not fully follow the properties of the lipids membrane . 4. The membrane should be resistant to proteolysis of the transmembrane regions, allowing determination of their abundance. 5. The transmembrane peptides will be either mainly or may not be hydrophobic.