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  • 1. Kwak, Young-Keun
    et al.
    Högbom, Martin
    Colque-Navarro, Patricia
    Möllby, Roland
    Vécsey-Semjén, Beatrix
    KTH.
    Biological Relevance of Natural alpha-Toxin Fragments from Staphylococcus aureus2010In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 233, no 1-3, p. 93-103Article in journal (Refereed)
    Abstract [en]

    Serine proteases represent an essential part of cellular homeostasis by generating biologically active peptides. In bacteria, proteolysis serves two different roles: a major housekeeping function and the destruction of foreign or target cell proteins, thereby promoting bacterial invasion. In the process, other virulence factors such as exotoxins become affected. In Staphylococcus aureus culture supernatant, the pore-forming alpha-toxin is cleaved by the coexpressed V8 protease and aureolysin. The oligomerizing and pore-forming abilities of five such spontaneously occurring N- and C-terminal alpha-toxin fragments were studied. H-3-marked alpha-toxin fragments bound to rabbit erythrocyte membranes but only fragments with intact C termini, missing 8, 12 and 71 amino acids from their N-terminal, formed stable oligomers. All isolated fragments induced intoxication of mouse adrenocortical Y1 cells in vitro, though the nature of membrane damage for a fragment, degraded at its C terminus, remained obscure. Only one fragment, missing the first eight N-terminal amino acids, induced irreversible intoxication of Y1 cells in the same manner as the intact toxin. Four of the isolated fragments caused swelling, indicating altered channel formation. Fragments missing 12 and 71 amino acids from the N terminus occupied the same binding sites on Y1 cell membranes, though they inhibited membrane damage caused by intact toxin. In conclusion, N-terminal deletions up to 71 amino acids are tolerated, though the kinetics of channel formation and the channel's properties are altered. In contrast, digestion at the C terminus results in nonfunctional species.

  • 2. Purhonen, P.
    et al.
    Thomsen, K.
    Maunsbach, A. B.
    Hebert, Hans
    KTH, School of Technology and Health (STH), Structural Biotechnology.
    Association of renal Na,K-ATPase alpha-subunit with the beta- and gamma-subunits based on cryoelectron microscopy2006In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 214, no 3, p. 139-146Article in journal (Refereed)
    Abstract [en]

    Na,K-ATPase transports Na+ and K+ across cell membranes and consists of alpha- and beta-subunits. Na,K-ATPase also associates with small FXYD proteins that regulate the activity of the pump. We have used cryoelectron microscopy of two-dimensional crystals including data to 8 A resolution to determine the three-dimensional (3-D) structure of renal Na,K-ATPase containing FXYD2, the gamma-subunit. A homology model for the a- subunit was calculated from a Ca2+-ATPase structure and used to locate the additional beta- and gamma-subunits present in the 3-D map of Na,K-ATPase. Based on the 3-D map, the beta- subunit is located close to transmembrane helices M8 and M10 and the gamma-subunit is adjacent to helices M2 and M9 of the alpha-subunit.

  • 3. Purhonen, P
    et al.
    Thomsen, K
    Maunsbach, AB
    Hebert, Hans
    Karolinska Institutet.
    Association of renal Na,K-ATPase a-subunit with the b- and g-subunits based on cryo-electron microscopy2007In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 214, p. 139-146Article in journal (Refereed)
  • 4.
    Vécsey-Semjén, Beatrix
    et al.
    KTH.
    Kwak, Young-Keun
    Högbom, Martin
    Möllby, Roland
    Channel-Forming Abilities of Spontaneously Occurring alpha-Toxin Fragments from Staphylococcus aureus2010In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 234, no 3, p. 171-181Article in journal (Refereed)
    Abstract [en]

    Pore formation by four spontaneously occurring alpha-toxin fragments from Staphylococcus aureus were investigated on liposome and erythrocyte membranes. All the isolated fragments bound to the different types of membranes and formed transmembrane channels in egg-phosphatidyl glycerol vesicles. Fragments of amino acids (aa) 9-293 (32 kD) and aa 13-293 (31 kD) formed heptamers, similar to the intact toxin, while the aa 72-293 (26 kD) fragment formed heptamers, octamers, and nonamers, as judged by gel electrophoresis of the liposomes. All isolated fragments induced release of chloride ions from large unilamellar vesicles. Channel formation was promoted by acidic pH and negatively charged lipid head groups. Also, the fragments' hemolytic activity was strongly decreased under neutral conditions but could be partially restored by acidification of the medium. We paid special attention to the 26-kD fragment, which, despite the loss of about one-fourth of the N-terminal part of alpha-toxin, did form transmembrane channels in liposomes. In light of the available data on channel formation by alpha-toxin, our results suggest that proteolytic degradation might be better tolerated than previously reported. Channel opening could be inhibited and open channels could be closed by zinc in the medium. Channel closure could be reversed by addition of EDTA. In contrast, digestion at the C terminus led to premature oligomerization and resulted in species with strongly diminished activity and dependent on protonation.

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