Biology subjects

Perez, M. E.

Publications and source records attributed to Perez, M. E..

3 recordsLinked to original sources

bioRxiv2024

Binding of PUFA stabilizes a conductive state of the selectivity filter in IKs channels

In cardiomyocytes, the KCNQ1/KCNE1 channel complex mediates the slow delayed-rectifier current (IKs), pivotal during the repolarization phase of the ventricular action potential. Mutations in IKs cause Long QT Syndrome (LQTS), a syndrome with a prolonged QT interval on the ECG, which increases the risk of ventricular arrhythmia and sudden cardiac death. One potential therapeutical intervention for LQTS is based on targeting IKs channels to restore channel function and/or the physiological QT interval. Polyunsaturated fatty acids (PUFAs) are potent activators of KCNQ1 channels and activate IKs channels by binding to two different sites, one in the voltage sensor domain (VSD) - which shifts the voltage dependence to more negative voltages- and the other in the pore domain (PD) - which increases the maximal conductance of the channels (Gmax). However, the mechanism by which PUFAs increase the Gmax of the IKs channels is still poorly understood. In addition, it is unclear why IKs channels have a very small single channel conductance and a low open probability or whether PUFAs affect any of these properties of IKs channels. Our results suggest that the selectivity filter in KCNQ1 is normally unstable, contributing to the low open probability, and that the PUFA-induced increase in Gmax is caused by a stabilization of the selectivity filter in an open-conductive state.

biophysics↗

bioRxiv2023

A solid beta-sheet structure is formed at the surface of FUS liquid droplets during aging

Insights into liquid droplet formation via liquid-liquid phase separation and the subsequent liquid-to-solid phase transition are important for understanding cell dynamics, as well as a number of neurodegenerative disorders. We report here, using the example of the FUsed in Sarcoma (FUS) protein, an investigation of the liquid droplet maturation process combining solution- and solid-state NMR spectroscopy, Raman spectroscopy, and light and electron microscopies. Our study reveals that the surface of the droplets plays a critical role in this process. Indeed, when comparing a biphasic sample, in which liquid droplets are stabilized in an agarose matrix, with a pure monophasic condensed phase sample, we find that the liquid-droplet maturation kinetics is faster in the biphasic FUS sample, owing to the larger surface-to-volume ratio. In addition, using Raman spectroscopy, we observe structural differences upon liquid-droplet maturation between the inside and the surface of liquid droplets, which is of {beta}-sheet content as revealed by solid-state NMR. This is detected very early on and increases over time. In agreement with these observations, a solid crust-like shell is visually seen by microaspiration experiments. After several months, electron microscopy reveals that the matured FUS droplets have converted into solid linear fibrils distinct from the fibril core of seeded fibrils reported previously, as arginine side-chains from the arginine-and-glycine-rich domain (RGG) motif are partially rigidified, highlighting the participation of this motif in the liquid-to-solid transition. In presence of RNA, this aging process is not taking place.

biochemistry↗

bioRxiv2022

Distinctive mechanisms of epilepsy-causing mutants discovered by measuring S4 movement in KCNQ2 channels

Neuronal KCNQ channels mediate the muscarine-regulated M-current, a key regulator of membrane excitability in the central and peripheral nervous systems. Mutations in KCNQ2 channels cause severe neurodevelopmental disorders, including epileptic encephalopathies. However, the impact that mutations have on channel function remain poorly defined, largely because of our limited understanding of the voltage sensing mechanisms that trigger channel gating. Here, we present measurements of voltage sensor movements in wt-KCNQ2 and channels bearing epilepsy-causing mutations using mutagenesis, cysteine accessibility, and voltage clamp fluorometry (VCF). Cysteine modification reveals that a stretch of 8-9 amino acids in the S4 become exposed upon opening of KCNQ2 channels. VCF shows that the voltage dependence and kinetics of S4 movement and channel opening/closing closely correlate, suggesting an activation scheme in which channel opening does not require multiple voltage-sensor movements. VCF and kinetic modeling reveal different mechanisms by which epilepsy-causing mutations affect KCNQ2 channel voltage-dependent gating. This study provides insight into KCNQ2 channel function, which will aid in uncovering the mechanisms underlying channelopathies.

biophysics↗