title: The solution structure and oligomerization behavior of two bacterial toxins: pneumolysin and perfringolysin O.
abstract: Pneumolysin (PLY), an important protein virulence factor of the human bacterial pathogen Streptococcus pneumoniae, could be a candidate for inclusion in a new anti-streptococcal vaccine. PLY solution species from monomer via multimeric intermediates to ring-shaped oligomers were studied with time-dependent sedimentation velocity in the analytical ultracentrifuge (AUC). Hydrodynamic bead modeling was used to interpret the data obtained. PLY remained mostly monomeric in solution; intermediate PLY multimers were detected in small quantities. Current understanding of PLY molecular mechanism is guided by a model built on the basis of its homology with perfringolysin O (PFO) for which there is an atomic structure. PFO, a virulence factor of the organism Clostridium perfringens, has almost the same molecular mass as PLY and shares 48% sequence identity and 60% sequence similarity with PLY. We report a comparative low-resolution structural study of PLY and PFO using AUC and small-angle x-ray scattering (SAXS). AUC data demonstrate that both proteins in solution are mostly monodisperse but PLY is a monomer whereas PFO is mostly dimeric. Ab initio dummy atom and dummy residue models for PFO and PLY were restored from the distance distribution function derived from experimental small-angle x-ray scattering curves. In solution, PLY is elongated, consistent with the shape predicted by its high-resolution homology model. The PFO dimer is also an elongated particle whose shape and volume are consistent with a staggered antiparallel dimer.
authors.affiliation: Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland. alexandra.solovyova@bio.gla.ac.uk
authors.forename: Alexandra S
authors.initials: AS
authors.lastname: Solovyova
authors.forename: Marcelo
authors.initials: M
authors.lastname: Nöllmann
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Mitchell
authors.forename: Olwyn
authors.initials: O
authors.lastname: Byron
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D001427:Bacterial Toxins / Q000737:chemistry*; D003016:Clostridium perfringens / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D006460:Hemolysin Proteins; D008958:Models, Molecular; D013296:Streptococcus pneumoniae / Q000737:chemistry*; D013301:Streptolysins / Q000737:chemistry*; D014461:Ultracentrifugation
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D013301:Streptolysins; C032290:plY protein, Streptococcus pneumoniae; C020452:Clostridium perfringens theta-toxin