Biology subjects

Hengel, F. E.

Publications and source records attributed to Hengel, F. E..

2 recordsLinked to original sources

bioRxiv2020

Measurement of hindered diffusion in complex geometries for high-speed single-molecule experiments

In a high-speed single-molecule experiment, a protein is tethered between two substrates that are manipulated to exert force on the system. To avoid nonspecific interactions between the protein and nearby substrates, the protein is usually attached to the substrates through long, flexible linkers. This approach precludes measurements of mechanical properties with high spatial and temporal resolution, for rapidly exerted forces are dissipated into the linkers. Because mammalian hearing operates at frequencies reaching tens to hundreds of kilohertz, the mechanical processes that occur during transduction are of very short duration. Single-molecule experiments on the relevant proteins therefore cannot involve long tethers. We previously characterized the mechanical properties of protocadherin 15 (PCDH15), a protein essential for human hearing, by tethering an individual monomer through very short linkers between a probe bead held in an optical trap and a pedestal bead immobilized on a glass coverslip. Because the two confining surfaces were separated by only the length of the tethered protein, hydrodynamic coupling between those surfaces complicated the interpretation of the data. To facilitate our experiments, we characterize here the anisotropic and position-dependent diffusion coefficient of a probe in the presence of an effectively infinite wall, the coverslip, and of the immobile pedestal.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biophysics↗

bioRxiv2018

The elasticity of individual protocadherin 15 molecules implicates cadherins as the gating springs for hearing

Hair cells, the sensory receptors of the inner ear, respond to mechanical forces originating from sounds and accelerations1,2. An essential feature of each hair cell is an array of filamentous tip links, consisting of the proteins protocadherin 15 (PCDH15) and cadherin 23 (CDH23)3, whose tension is thought to directly gate the cells transduction channels4,5,6. These links are considered far too stiff to represent the gating springs that convert hair-bundle displacement into forces capable of opening the channels7,8, and no mechanism has been suggested through which tip-link stiffness could be varied to accommodate hair cells of distinct frequency sensitivity in different receptor organs and animals. As a consequence, the gating springs identity and mechanism of operation remain central questions in sensory neuroscience. Using a high-precision optical trap, we show that an individual monomer of PCDH15 acts as an entropic spring that is much softer than its enthalpic stiffness alone would suggest7,8. This low stiffness implies that the protein is a significant part of the gating spring that controls a hair cells transduction channels. The tip links entropic nature then allows for stiffness control through modulation of its tension. We find that a PCDH15 molecule is unstable under tension and exhibits a rich variety of reversible unfolding events that are augmented when the Ca2+ concentration is reduced to physiological levels. Tip-link tension and Ca2+ concentration are therefore likely parameters through which nature tunes a gating springs mechanical properties.

biophysics↗