Protein penetration

Gupta B, Levchenko TS, Torchilin VP. Intracellular delivery of large molecules and small particles by cell-penetrating proteins and peptides. Adv Drug Deliver Rev 2005 57 637. 

The second observation which does not support the unfolded protein model is that when phospholipase A (N. naja venom) was injected into the subphase under the lipid monolayer at equilibrium with globulin, lecithin was readily attacked, as indicated by the rapid fall of surface potential (4, 5, 6). If the penetrated protein were to cover entirely the polar groups of the lipid facing the aqueous subphase (as postulated in the unfolded protein model), the lipid molecules should not be accessible to the lipolytic enzyme. 

T. S., and Torchilin, V.R, Intracellular delivery of large molecules and small particles by cell-penetrating proteins and peptides, Adv. Drug Deliv. Rev. 57, 637-651, 2005 Deshayes, S., Morris, M.C., Divta, G., and Heitz, R, Cell-penetrating peptides tools for intracellular delivery of therapeutics. Cell. Mol. Life Sci. 62, 1839-1849, 2005. See Amphipathic. 

Fig. 2.19 Diagram of the plasma membrane showing its integral proteins (fluid mosaic model) (adapted from S.J. Singer et af, 1972 and H. Knufermann, 1976). 1 external aqueous milieu, 2 internal aqueous milieu, 3 fracture plane of the apolar membrane layer, 4 externally orientated intrinsic protein (ectoprotein), 5 internally orientated intrinsic protein (endoprotein), 6 external extrinsic protein, 7 internal intrinsic protein, 8, 9 membrane-penetrating proteins with hydrophobic interactions in the inside of the membrane (P = polar region), 10 membrane pervaded by glycoprotein with sugar residues (, 11 lateral diffusion (A) and flip-flop (B), 12 hydrophilic region (A) and hydrophobic region (B) of the bilayer membrane...

Neutral red dye penetration Protein leakage, colorimetric assay Coomassi Blue or Kenacid Blue for cell proliferation protein synthesis... 

Penetration of Human Serum Albumin into Phosphatidylserine Monolayers. We have tried to analyze quantitatively the results of Kimelberg and Papahadjopoulos (7) of protein penetration in phospholipid monolayers. These authors did not measure the surface density of the penetrating protein. They studied the system phosphatidylserine monolayer—human serum albumin (HSA) at different pH values. When the pH was 7.4, the protein and the lipid repelled each other. When the... 

Furthermore, since the protein concentration used in the substrate was very high, one can consider that the mixed monolayer has been saturated with the penetrating protein. Then the mixing terms may be the same at both pH values. 

Unfortunately a quantitative discussion of their results is impossible since the surface densities of the penetrating protein were not measured. 

It is simple to describe the stoichiometry of a mixed lipid-protein film after protein adsorption is complete if the penetrating protein molecules simply act as a mechanical barrier and compress the lipid molecules in the manner used to obtain ir-A curves. The mixed film is described by a geometric model in which the area per lipid molecules decreases from tti to (tti + A7r) consistent with the ir-A isotherm of the lipid. The adsorption of the hydrophobic /3-casein molecules to lecithin monolayers (12) can be described by this model if additional condensation of the lipid and/or protein is included. The degree of condensation is a function of Cp the lipid-protein mole ratios in the mixed films (data in Figures 2 and 3) range from ca. 500 1 to 50 1. 

Some of the proteins that span the bilayer seem to be coiled rods, as detected by freeze-fracture, whereas others appear to be globular (see Fig. 5.5). Most, possibly all, of these penetrating proteins have an attached carbohydrate molecule, which remains on the cytoplasmic side, apparently serving as a hydrophilic anchor for the protein. 

Fig. 1.2. Membrane proteins extrinsic protein (a) intrinsic proteins penetrating proteins [ectoprotein (b), endoprotein (c)], spanning protein (d), included protein (e).

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