Evidence for membrane affinity of the C-terminal domain of bovine milk PP3 component.
Component PP3 is a phosphoglycoprotein isolated from bovine milk with unknown biological function, which displays in its C-terminal region a basic amphipathic alpha-helix, a feature often involved in membrane association. According to that, the behaviour of PP3 and of a synthetic peptide from the C-terminal domain (residues 113-135) was investigated in lipid environment. Conductance measurements indicated that the peptide was able to associate and form channels in planar lipid bilayers composed of neutral or charged phospholipids. Electrostatic interactions seemed to promote voltage-dependent channel formation but this was not absolutely required since the pore-forming ability of the 113-135 C-terminal peptide was also detected with the zwitterionic lipid bilayer. Additionally, a spectroscopic study using circular dichroism argues that the peptide adopts an alpha-helical conformation in interaction with neutral or charged micelles. Thus, the conducting aggregates in bilayers might be composed of a bundle of peptides in helical conformation. Besides, similar conductance measurements performed with the whole PP3 protein did not induce any channel fluctuations. However, with the latter, an early breakdown of the bilayers occurred, a finding that can be tentatively explained by a massive incorporation of PP3. In the light of the present results, it could be inferred that PP3 membrane attachment may be achieved by oligomerization of the C-terminal amphipathic helical region.
Campagna
S
S
Laboratoire des Biosciences de l'Aliment, UA INRA 885, Université Henri Poincaré, Nancy-1, BP 239, 54506 Vandoeuvre-lès-Nancy Cedex, France. campagna@scbiol.uhp-nancy.fr
Cosette
P
P
Molle
G
G
Gaillard
J L
JL
D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D002942:Circular Dichroism; D004553:Electric Conductivity; D006023:Glycoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D011487:Protein Conformation
D002364:Caseins; D006023:Glycoproteins; D008051:Lipid Bilayers; C085522:PP3 protein, Bos taurus; D010446:Peptide Fragments; D010750:Phosphoproteins