PROJECT SUMMARY/ABSTRACT The lab recently discovered a family of proton-selective ion channels collectively known as the Otopetrins. The protein family was first identified based on the essential role of OTOP1 in the development of the vestibular system, but their function as proton channels was not known. Functions ascribed to OTOP channels since their discovery include pH sensing in the taste system of both vertebrates and invertebrates and biomineralization in the development of the invertebrate skeleton and vertebrate otoconia. OTOP channels have been found in the digestive tract where they may play a role in pH sensing or acid transport, and where their expression is correlated with disease prognosis. This application is to fund multidisciplinary approaches in the Liman lab aimed at uncovering the basic functional properties of OTOP channels and describing their distribution in vertebrate and invertebrate systems, with the ultimate goal of understanding the role of OTOP channels in non-sensory systems. The proposal focuses mainly on vertebrate OTOP2 and OTOP3 and on invertebrate OTOPS, whose function and distribution are poorly understood. In the last grant period, the lab showed that OTOP3 is gated by H+ and Zn2+ while OTOP2 is constitutively open. Using chimeras between the channels, we were able to begin to identify elements of the gating apparatus. In the next grant period, the lab will examine, in increasing detail, the functional properties of OTOP2 and OTOP3 channels that are relevant to their physiological roles. The structural basis for functional properties of OTOP2 and OTOP3 channels, such as the mechanism of Zn2+ potentiation, will be determined using structure-guided site-directed mutagenesis. Moreover, we will develop and test mouse strains that allow us to visualize the distribution of OTOP channels and test their functional roles. A goal of the research is to discover basic principles that govern the function of this novel class of ion channels and to identify commonalities that will lead to an understanding of their functions in different cellular contexts. Because OTOP2 and OTOP3 channels are not yet associated closely with a physiological process or disease, funding from NIGMS is critical to support these fundamental studies.

PROJECT NARRATIVE Otopetrin (OTOP) channels conducts protons across cell membranes and are found throughout the body, including in the digestive tract where their expression has been correlated with disease progression. This funding will support a multidisciplinary approach using powerful biophysical and genetic and imaging methods to characterize the subcellular distribution, gating and permeation properties of OTOP2 and OTOP3 channels with the goal of shedding light on their physiological functions in health and disease.