Aggregatibacter actinomycetemcomitans leukotoxin cytotoxicity occurs through bilayer destabilization.
The Gram-negative bacterium, Aggregatibacter actinomycetemcomitans, is a common inhabitant of the human upper aerodigestive tract. The organism produces an RTX (Repeats in ToXin) toxin (LtxA) that kills human white blood cells. LtxA is believed to be a membrane-damaging toxin, but details of the cell surface interaction for this and several other RTX toxins have yet to be elucidated. Initial morphological studies suggested that LtxA was bending the target cell membrane. Because the ability of a membrane to bend is a function of its lipid composition, we assessed the proficiency of LtxA to release of a fluorescent dye from a panel of liposomes composed of various lipids. Liposomes composed of lipids that form nonlamellar phases were susceptible to LtxA-induced damage while liposomes composed of lipids that do not form non-bilayer structures were not. Differential scanning calorimetry demonstrated that the toxin decreased the temperature at which the lipid transitions from a bilayer to a nonlamellar phase, while (31) P nuclear magnetic resonance studies showed that the LtxA-induced transition from a bilayer to an inverted hexagonal phase occurs through the formation of an isotropic intermediate phase. These results indicate that LtxA cytotoxicity occurs through a process of membrane destabilization.
Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA.
Angela C
AC
Brown
Kathleen
K
Boesze-Battaglia
Yurong
Y
Du
Frank P
FP
Stefano
Irene R
IR
Kieba
Raquel F
RF
Epand
Lazaros
L
Kakalis
Philip L
PL
Yeagle
Richard M
RM
Epand
Edward T
ET
Lally
D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D048430:Cell Shape / Q000187:drug effects; D005098:Exotoxins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D005452:Fluoresceins / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D006801:Humans; D019169:Jurkat Cells; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008871:Microvilli / Q000187:drug effects / Q000648:ultrastructure; D015661:Pasteurellaceae; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry
D001427:Bacterial Toxins; D005098:Exotoxins; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C018579:leukotoxin; C007740:fluorexon