Reversible molecular motional switch based on circular photoactive protein oligomers exhibits unexpe
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Lee, Sang Jin↗
Engineering topics
Hyun, Jaekyung
Publications and source records attributed to Hyun, Jaekyung.
Cations Modulate Actin Bundle Mechanics, Assembly Dynamics, and Structure
Actin bundles are key factors in the mechanical support and dynamic reorganization of the cytoskeleton. High concentrations of multivalent counterions promote bundle formation through electrostatic attraction between actin filaments that are negatively charged polyelectrolytes. In this study, we evaluate how physiologically relevant divalent cations affect the mechanical, dynamic, and structural properties of actin bundles. Using a combination of total internal reflection fluorescence microscopy, transmission electron microscopy, and dynamic light scattering, we demonstrate that divalent cations modulate bundle stiffness, length distribution, and lateral growth. Molecular dynamics simulations of an all-atom model of the actin bundle reveal specific actin residues coordinate cation-binding sites that promote the bundle formation. Finally, our work suggests that specific cation interactions may play a fundamental role in the assembly, structure, and mechanical properties of actin bundles.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Stoichiometry and mechanistic implications of the MacAB-TolC tripartite efflux pump
Highlights: • The exact stoichiometry of the MacAB-TolC pump was confirmed. • Structural comparison provides a mechanism for MacA-dependent MacB activation. • Improving understanding of the regulatory mechanisms of other efflux pumps. The MacAB-TolC tripartite efflux pump is involved in resistance to macrolide antibiotics and secretion of protein toxins in many Gram-negative bacteria. The pump spans the entire cell envelope and operates by expelling substances to extracellular space. X-ray crystal and electron microscopic structures have revealed the funnel-like MacA hexamer in the periplasmic space and the cylindrical TolC trimer. Nonetheless, the inner membrane transporter MacB still remains ambiguous in terms of its oligomeric state in the functional complex. In this study, we purified a stable binary complex using a fusion protein of MacA and MacB of Escherichia coli, and then supplemented MacA to meet the correct stoichiometry between the two proteins. The result demonstrated that MacB is a homodimer in the complex, which is consistent with results from the recent complex structure using cryo-electron microscopy single particle analysis. Structural comparison with the previously reported MacB periplasmic domain structure suggests a molecular mechanism for regulation of the activity of MacB via an interaction between the MacB periplasmic domain and MacA. Our results provide a better understanding of the tripartite pumps at the molecular level.
60 APPLIED LIFE SCIENCES↗