title: Surface dependence of protein nanocrystal formation.
abstract: The self-assembly kinetics and nanocrystal formation of the bacterial surface-layer-protein SbpA are studied with a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Silane coupling agents, aminopropyltriethoxysilane (APTS) and octadecyltrichlorosilane (OTS), are used to vary the protein-surface interaction in order to induce new recrystallization pathways. The results show that the final S-layer crystal lattice parameters (a = b = 14 nm, gamma = 90 degrees ), the layer thickness (15 nm), and the adsorbed mass density (1700 ng cm(-2)) are independent of the surface chemistry. Nevertheless, the adsorption rate is five times faster on APTS and OTS than on SiO(2,) strongly affecting protein nucleation and growth. As a consequence, protein crystalline domains of 0.02 microm(2) for APTS and 0.05 microm(2) for OTS are formed, while for silicon dioxide the protein domains have a typical size of about 32 microm(2). In addition, more-rigid crystalline protein layers are formed on hydrophobic substrates. In situ AFM experiments reveal three different kinetic steps: adsorption, self-assembly, and crystalline-domain reorganization. These steps are corroborated by frequency-dissipation curves. Finally, it is shown that protein adsorption is a diffusion-driven process. Experiments at different protein concentrations demonstrate that protein adsorption saturates at 0.05 mg mL(-1) on silane-coated substrates and at 0.07 mg mL(-1) on hydrophilic silicon dioxide.
authors: Biosurfaces Unit, CIC biomaGUNE Paseo Miramón 182, 20009 San Sebastián, Spain.
authors: Aitziber Eleta
authors: AE
authors: Lopez
authors: Susana
authors: S
authors: Moreno-Flores
authors: Dietmar
authors: D
authors: Pum
authors: Uwe B
authors: UB
authors: Sleytr
authors: José L
authors: JL
authors: Toca-Herrera
mesh_terms: D000327:Adsorption; D001426:Bacterial Proteins / Q000737:chemistry*; D003460:Crystallization; D018625:Microscopy, Atomic Force; D009004:Monosaccharide Transport Proteins / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D011791:Quartz / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D009004:Monosaccharide Transport Proteins; C120455:SbpA protein, bacteria; D012821:Silanes; D011791:Quartz