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    In Vitro Characterization of the Two-Stage Non-Classical Reassembly Pathway of S-Layers

    Year: 2017

    Journal: Int. J. Mol. Sci., Volume 18, FEB

    Authors: Breitwieser, Andreas; Iturri, Jagoba; Toca-Herrera, Jose-Luis; Sleytr, Uwe B.; Pum, Dietmar

    Keywords: S-layer proteins; two-step crystallization; self-assembly kinetics; non-classical crystal growth; Ca2+ binding

    The recombinant bacterial surface layer (S-layer) protein rSbpA of Lysinibacillus sphaericus CCM 2177 is an ideal model system to study non-classical nucleation and growth of protein crystals at surfaces since the recrystallization process may be separated into two distinct steps: (i) adsorption of S-layer protein monomers on silicon surfaces is completed within 5 min and the amount of bound S-layer protein sufficient for the subsequent formation of a closed crystalline monolayer; (ii) the recrystallization process is triggeredafter washing away the unbound S-layer proteinby the addition of a CaCl2 containing buffer solution, and completed after approximately 2 h. The entire self-assembly process including the formation of amorphous clusters, the subsequent transformation into crystalline monomolecular arrays, and finally crystal growth into extended lattices was investigated by quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM). Moreover, contact angle measurements showed that the surface properties of S-layers change from hydrophilic to hydrophobic as the crystallization proceeds. This two-step approach is new in basic and application driven S-layer research and, most likely, will have advantages for functionalizing surfaces (e.g., by spray-coating) with tailor-made biological sensing layers.
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