title: Fold-unfold transitions in the selectivity and mechanism of action of the N-terminal fragment of the bactericidal/permeability-increasing protein (rBPI(21)).
abstract: Septic or endotoxic shock is a common cause of death in hospital intensive care units. In the last decade numerous antimicrobial peptides and proteins have been tested in the search for an efficient drug to treat this lethal disease. Now in phase III clinical trials, rBPI(21), a recombinant N-terminal fragment of the bactericidal/permeability-increasing protein (BPI), is a promising drug to reduce lesions caused by meningococcal sepsis. We correlated structural and stability data with functional information of rBPI(21) bound to both model systems of eukaryotic and bacterial membranes. On interaction with membranes, rBPI(21) loses its conformational stability, as studied by circular dichroism. This interaction of rBPI(21) at membrane level was higher in the presence of negatively charged phospholipid relatively to neutral ones, with higher partition coefficients (K(p)), suggesting a preference for bacterial membranes over mammalian membranes. rBPI(21) binding to membranes is reinforced when its disulfide bond is broken due to conformational changes of the protein. This interaction is followed by liposome aggregation due to unfolding, which ensures protein aggregation, and interfacial localization of rBPI(21) in membranes, as studied by extensive quenching by acrylamide and 5-deoxylstearic acid and not by 16-deoxylstearic acid. An uncommon model of the selectivity and mechanism of action is proposed, where membrane induces unfolding of the antimicrobial protein, rBPI(21). The unfolding ensures protein aggregation, established by protein-protein interaction at membrane surface or between adjacent membranes covered by the unfolded protein. This protein aggregation step may lead to membrane perturbation.
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal.
authors.forename: Marco M
authors.initials: MM
authors.lastname: Domingues
authors.forename: Sílvia C D N
authors.initials: SC
authors.lastname: Lopes
authors.forename: Nuno C
authors.initials: NC
authors.lastname: Santos
authors.forename: Alexandre
authors.initials: A
authors.lastname: Quintas
authors.forename: Miguel A R B
authors.initials: MA
authors.lastname: Castanho
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000737:chemistry*; D001798:Blood Proteins / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry; D008027:Light; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D017510:Protein Folding; D055550:Protein Stability / Q000187:drug effects; D011994:Recombinant Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D013696:Temperature; D014867:Water / Q000494:pharmacology
chemical_list: D023181:Antimicrobial Cationic Peptides; D001798:Blood Proteins; D004220:Disulfides; D008051:Lipid Bilayers; D008070:Lipopolysaccharides; D010446:Peptide Fragments; D010743:Phospholipids; D011994:Recombinant Proteins; C021623:bactericidal permeability increasing protein; D014867:Water