Determination of protein surface excess on a liquid/solid interface by single-molecule counting

In silico modeling of the pore region of a KCNQ4 missense mutant from a patient with hearing loss

Background

Mutation of the voltage-gated potassium channel KCNQ4 causes DFNA2-type nonsyndromic autosomal dominant sensorineural hearing loss. KCNQ4 is expressed predominantly in the auditory sensory outer hair cells, which are critical for sound amplification.

Results

We sequenced KCNQ4 from Japanese patients with sensorineural hearing loss, and identified a novel missense mutation encoding a Tyr270His located at the N-terminus of the highly conserved pore helix sequence. As this patient was not accessible to us and information about them was limited, we used molecular modeling to investigate whether this novel mutation is hypothetically pathogenic. A careful examination of an in silico structural model of the KCNQ4 pore region revealed that the Tyr270His mutation caused an alteration in the electrostatic surface potential of the pore helix.

Conclusion

We propose two possible means by which the Tyr270His mutation causes hearing loss: a positively charged His270 side chain might enhance the helix dipole moment of the pore helix, thereby destabilizing the helix and/or the pore region, or it might disturb transport of K⁺ through the channel by electrostatic repulsion.

Observing photophysical properties of quantum dots in air at the single molecule level: advantages in microarray applications

Quantum dots (QDs) are promising fluorescent tags for microarrays. Because most microarrays are analyzed under dry conditions, it is necessary to examine the photo properties of QDs in air. We demonstrate that the photophysical characteristics of individual quantum dots are different at the liquid/solid interface compared with QDs at the air/solid interface by observing them through a wide-field fluorescence microscope. QDs in air show higher photo-stability, higher fluorescence signal, slower spectral blue shift rate, less blinking and shorter bulk fluorescence lifetime than those in solution. These beneficial properties indicate QDs are good alternative fluorescent probes for microarrays.