Electrical sensing
As a paradigm of detection of electrical stimuli, we study proteins containing voltage-sensing domains (VSDs). These domains are made of four transmembrane segments and confer voltage sensitivity to channels that generate the action potential in nerves and muscles, as well as channels that modulate the production of reactive oxygen species by the NADPH oxidase, and voltage-dependent enzymes that dephosphorylate phosphoinositide lipids. In collaboration with the Tobias lab, we are studying the voltage-gated proton channel Hv1, which contains two proton-conducting VSDs held together by a cytoplasmic coiled-coil domain. The excessive activity of this channel can lead to cancer development, neuroinflammation, and brain damage after ischemic stroke. Hv1 inhibitors could find applications as anticancer drugs and neuroprotective agents. We have developed small-molecule inhibitors of the channel, which we use to explore the mechanisms of gating and the interaction between VSDs and small molecule ligands. In collaboration with the Pearlman lab, we are using the inhibitors to study the role of Hv1 in inflammation.
Mechanical sensing
As a paradigm of detection of mechanical cues, we study the Piezo proteins, which are calcium-permeable cation channels activated by membrane stretch. Piezo channels play important roles in mechanosensory pain and touch sensing, as well as in erythrocyte volume regulation, epithelial crowding, cell migration, and detection of blood flow. In collaboration with the Pathak and Flanagan labs, we found that the Piezo1 channel is expressed by human neural stem progenitor cells (hNSPCs) where it is responsible for calcium influx triggered by traction forces. Piezo1-mediated calcium transients depend on the stiffness of the microenvironment and direct mechanosensitive lineage specification of hNSPCs. The ongoing collaboration aims to elucidate the mechanism underlying the activation of Piezo1 by cell-generated mechanical forces. Unlike Piezo1, the Hv1 channel is not mechanically gated. Nonetheless, its voltage dependent activation is potentiated by membrane stretch. We have recently proposed a mechanism linking the potentiation of microglial Hv1 by cell-swelling to brain damage after stroke and are currently investigating the molecular determinants of Hv1 mechanosensitivity.
Engineering new sensors
Applying what we learn about the mechanisms of ion channel gating, we endeavor to generate GPCR-ion channel hybrid proteins that are capable of directly transducing chemical cues into an electrical current. In collaboration with the Burke lab, we are engineering odorant receptors (ORs) to be covalently linked to the pore domain of potassium channels to generate a device that functions as an “artificial nose.” Examples of chemical cues that can be detected are volatile compounds for quality control of food and healthcare products, as well as explosives and environmental toxins. Since the sensor is electronic, it could be integrated into a system in which signal recognition is based on hundreds of different sensors in one chip. Our lab is particularly interested in understanding how the conformational change associated with ligand binding in the OR, which normally would trigger trimeric G protein activation, can be harnessed to directly modulate the effector ion channel.