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  • 1.
    Jass, Jana
    et al.
    Örebro University, School of Science and Technology.
    Schedin, Staffan
    Fällman, Erik
    Ohlsson, Jörgen
    Nilsson, Ulf J.
    Uhlin, Bernt Eric
    Axner, Ove
    Physical properties of Escherichia coli P pili measured by optical tweezers2004In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 87, no 6, p. 4271-4283Article in journal (Refereed)
    Abstract [en]

    The mechanical behavior of individual P pili of uropathogenic Escherichia coli has been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of approximately 10(3) PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. They are particularly important in the pathogenesis of E. coli colonizing the upper urinary tract and kidneys. A biological model system has been established for in situ measurements of the forces that occur during mechanical stretching of pili. A mathematical model of the force-versus-elongation behavior of an individual pilus has been developed. Three elongation regions of pili were identified. In region I, P pili stretch elastically, up to a relative elongation of 16 +/- 3%. The product of elasticity modulus and area of a P pilus, EA, was assessed to 154 +/- 20 pN (n=6). In region II, the quaternary structure of the PapA rod unfolds under a constant force of 27 +/- 2 pN (n approximately 100) by a sequential breaking of the interactions between adjacent layers of PapA subunits. This unfolding can elongate the pilus up to 7 +/- 2 times. In region III, pili elongate in a nonlinear manner as a result of stretching until the bond ruptures.

  • 2.
    Koivuniemi, Artturi
    et al.
    VTT Bio- and Chemical Processes, Espoo, Finland.
    Sysi-Aho, Marko
    VTT Bio- and Chemical Processes, Espoo, Finland.
    Oresic, Matej
    Örebro University, School of Medical Sciences. VTT Bio- and Chemical Processes, Espoo, Finland.
    Ollila, Samuli
    Physical Chemistry, Lund University, Lund, Sweden.
    Interfacial properties of high-density lipoprotein-like lipid droplets with different lipid and apolipoprotein A-I compositions2013In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 10, p. 2193-2201, article id S0006-3495(13)00366-4Article in journal (Refereed)
    Abstract [en]

    The surface properties of high-density lipoproteins (HDLs) are important because different enzymes bind and carry out their functions at the surface of HDL particles during metabolic processes. However, the surface properties of HDL and other lipoproteins are poorly known because they cannot be directly measured for nanoscale particles with contemporary experimental methods. In this work, we carried out coarse-grained molecular dynamics simulations to study the concentration of core lipids in the surface monolayer and the interfacial tension of droplets resembling HDL particles. We simulated lipid droplets composed of different amounts of phospholipids, cholesterol esters (CEs), triglycerides (TGs), and apolipoprotein A-Is. Our results reveal that the amount of TGs in the vicinity of water molecules in the phospholipid monolayer is 25-50% higher compared to the amount of CEs in a lipid droplet with a mixed core of an equal amount of TG and CE. In addition, the correlation time for the exchange of molecules between the core and the monolayer is significantly longer for TGs compared to CEs. This suggests that the chemical potential of TG is lower in the vicinity of aqueous phase but the free-energy barrier for the translocation between the monolayer and the core is higher compared to CEs. From the point of view of enzymatic modification, this indicates that TG molecules are more accessible from the aqueous phase. Further, our results point out that CE molecules decrease the interfacial tension of HDL-like lipid droplets whereas TG keeps it constant while the amount of phospholipids varies.

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