Engineered covalent leucotoxin heterodimers form functional pores: insights into S-F interactions.
The staphylococcal alpha-toxin and bipartite leucotoxins belong to a single family of pore-forming toxins that are rich in beta-strands, although the stoichiometry and electrophysiological characteristics of their pores are different. The different known structures show a common beta-sandwich domain that plays a key role in subunit-subunit interactions, which could be targeted to inhibit oligomerization of these toxins. We used several cysteine mutants of both HlgA (gamma-haemolysin A) and HlgB (gamma-haemolysin B) to challenge 20 heterodimers linked by disulphide bridges. A new strategy was developed in order to obtain a good yield for S-S bond formation and dimer stabilization. Functions of the pores formed by 14 purified dimers were investigated on model membranes, i.e. planar lipid bilayers and large unilamellar vesicles, and on target cells, i.e. rabbit and human red blood cells and polymorphonuclear neutrophils. We observed that dimers HlgA T28C-HlgB N156C and HlgA T21C-HlgB T157C form pores with similar characteristics as the wild-type toxin, thus suggesting that the mutated residues are facing one another, allowing pore formation. Our results also confirm the octameric stoichiometry of the leucotoxin pores, as well as the parity of the two monomers in the pore. Correctly assembled heterodimers thus constitute the minimal functional unit of leucotoxins. We propose amino acids involved in interactions at one of the two interfaces for an assembled leucotoxin.
Laboratoire de Physiopathologie et d'Antibiologie Microbiennes, EA 3432, Institut de Bactériologie de la Faculté de Médecine (Université Louis Pasteur), Hôpitaux Universitaires de Strasbourg, 3 rue Koeberlé, F-67000 Strasbourg, France.
Olivier
O
Joubert
Gabriella
G
Viero
Daniel
D
Keller
Eric
E
Martinez
Didier A
DA
Colin
Henri
H
Monteil
Lionel
L
Mourey
Mauro
M
Dalla Serra
Gilles
G
Prévost
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism; D002463:Cell Membrane Permeability; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism*; D004912:Erythrocytes / Q000166:cytology / Q000378:metabolism; D005098:Exotoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D006460:Hemolysin Proteins; D006801:Humans; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D009504:Neutrophils / Q000166:cytology / Q000378:metabolism; D022022:Nuclear Pore / Q000737:chemistry* / Q000378:metabolism; D015202:Protein Engineering / Q000379:methods*; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D013997:Time Factors
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004220:Disulfides; D005098:Exotoxins; D006460:Hemolysin Proteins; D007473:Ion Channels; D011994:Recombinant Proteins; C037956:gamma-hemolysin, Staphylococcus aureus; C018579:leukotoxin; D003545:Cysteine