The mechanisms of interaction of the recombinant N-terminal portion of
bactericidal/permeability-increasing protein, rBPI21, with various planar asymmetric and symmetric bilayer membranes, including the
lipid matrix of the outer membrane of Gram-negative bacteria, were investigated via electrical measurements. For the
lipopolysaccharide (LPS) leaflet of the outer membrane, isolated deep rough mutant LPS of Escherichia coli strain F515 (F515 LPS) and Proteus mirabilis strain R45 (R45 LPS) were used. The addition of rBPI21 to the LPS side of asymmetric LPS/
phospholipid membranes, as well as to black
lipid membranes made from dioleoylphosphatidylglycerol (
DOPG), led to membrane
rupture. The innermembrane potential difference resulted in a slight increase from 0 to 5 mV for symmetric
DOPG membranes but changed for asymmetric F515 LPS/PL membranes from -36 to +8 mV and for R45 LPS/PL membranes from -37 to -5 mV following the addition of rBPI21. In all cases, the addition of rBPI21 led to an increase in membrane current. The effect of rBPI21 on the innermembrane potential difference of LPS/PL membranes was significantly reduced in the presence of 40 mM
MgCl2 (shift from -36 to -31 mV for F515 LPS). On the basis of these results and from our studies on the interaction of rBPI21 with
lipid monolayers and aggregates [Wiese, A., et al. (1997) Biochemistry 36, 10301-10310], a model is discussed explaining how the observed membrane
rupture, increase of membrane current, and change of transmembrane potential as induced by rBPI21 may contribute to bacterial dysfunction.