Abstract
Protein-surface interactions play a pivotal role in processes as diverse as biomineralization, biofouling, and the cellular response to medical implants. In biomineralization processes, biomacromolecules control mineral deposition and architecture via complex and often unknown mechanisms. For studying these mechanisms, the formation of magnetite nanoparticles in magnetotactic bacteria has become an excellent model system. Most interestingly, nanoparticle morphologies have been discovered that defy crystallographic rules (e.g., in the species Desulfamplus magnetovallimortis strain BW-1). In certain conditions, this strain mineralizes bullet-shaped magnetite nanoparticles, which exhibit defined (111) crystal faces and are elongated along the [100] direction. We hypothesize that surface-specific protein interactions break the nanoparticle symmetry, inhibiting the growth of certain crystal faces and thereby favoring the growth of others. Screening the genome of BW-1, we identified Mad10 (Magnetosome-associated deep-branching) as a potential magnetite-binding protein. Using atomic force microscope (AFM)-based single-molecule force spectroscopy, we show that a Mad10-derived peptide, which represents the most conserved region of Mad10, binds strongly to (100)- and (111)-oriented single-crystalline magnetite thin films. The peptide-magnetite interaction is thus material- but not crystal-face-specific. It is characterized by broad rupture force distributions that do not depend on the retraction speed of the AFM cantilever. To account for these experimental findings, we introduce a three-state model that incorporates fast rebinding. The model suggests that the peptide-surface interaction is strong in the absence of load, which is a direct result of this fast rebinding process. Overall, our study sheds light on the kinetic nature of peptide-surface interactions and introduces a new magnetite-binding peptide with potential use as a functional coating for magnetite nanoparticles in biotechnological and biomedical applications.
Highlights
U nderstanding the interaction between biomolecules and inorganic surfaces is of fundamental and applied interest in areas ranging from the control of crystal growth in synthetic and biological systems[1,2] to the synthesis of biocomposites,[3−5] biomedical implants,[6,7] and functional coatings.[8]
Using atomic force microscope (AFM)-based single-molecule force spectroscopy, we show that a Mad10-derived peptide, which represents the most conserved region of Mad[10], binds strongly to (100)- and (111)-oriented single-crystalline magnetite thin films
It has been hypothesized that specific proteins are responsible for this crystallography-defying morphology and that these proteins interact with certain crystal faces.[10,12,13]
Summary
Letter investigating the underlying molecular interactions and mechanisms. In MTB, proteins are known to control the size and organization of MNPs in specific organelles, termed magnetosomes. Letter not originate from multiple rupture events but are instead a characteristic of this specific Mad10p−magnetite interaction We hypothesize that these broad force distributions originate from one of the following three possibilities: the first possibility is the inherent heterogeneity originating from the magnetite thin films in the form of defects or different crystal faces. To obtain the probability density function of the rupture forces, we transform a master equation that describes the time evolution of the probability pi for the system to be in one of the three states (i) into a function of force: dp1(F) dF These equations involve the loading rate dF/dt that depends on the retraction speed and the nonlinear elastic properties of the PEG linker (see Supporting Information for details). According to the kinetic model, strong binding in the absence of force results from rapid exchange between the bound and intermediate states, with the equilibrium strongly shifted toward the bound state
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