ORCID
https://orcid.org/0009-0002-6755-2072
Date of Award
2026
Document Type
Dissertation
Degree Name
Philosophy (Ph.D)
Department
Biological Sciences
First Advisor
Yong Yu
Second Advisor
Ales Vancura
Third Advisor
Rachel Zufferey
Abstract
Proton-sensitive ion channels play essential roles in diverse physiological processes, including taste perception, epithelial transport, and cellular responses to changes in extracellular pH. Despite their physiological importance, the molecular mechanisms underlying proton-dependent activation and ion permeation remain incompletely understood. This dissertation investigates the functional and structural mechanisms of two distinct proton-sensitive ion channel systems: the human OTOP3 proton channels and the heteromeric PKD1L3/TRPP3 channel complex. The first project focused on the OTOP3, a member of the OTOP family of proton-selective ion channels. Although OTOP channels have recently been identified as proton channels involved in sour taste perception and other physiological processes, the functional properties of OTOP3 remained largely unexplored. In this study, electrophysiological analysis demonstrated that, compared to the other OTOP channels, human OTOP3 requires exceptionally strong extracellular acidification for activation, with robust channel activity observed only below pH 3.5. In addition to proton conduction, human OTOP3 exhibited a previously unrecognized mixed proton-anion current. Structure-guided mutagenesis further identified an extracellular loop that contributes to channel activation and ion permeation, providing new insights into the unique functional properties of the human OTOP3 channel and suggesting that it may be adapted to function in highly acidic microenvironments. The second project investigated the molecular basis of proton-dependent activation in the PKD1L3/TRPP3 heteromeric channel complex. Although PKD1L3/TRPP3 exhibits a characteristic acid-off response following strong extracellular acidification, the structural determinants responsible for this activation mechanism remain unknown. Guided by the recently resolved cryo-electron microscopy structure, structure-based mutagenesis identified H213 within the TRPP3 TOP domain as a critical determinant of channel activation. Functional analyses further demonstrated that the contribution of H213 depends on the extracellular architecture of PKD1L3, supporting a model in which proton-dependent gating is mediated by coordinated interactions across the extracellular regions of the heteromeric complex rather than by an isolated proton-sensing residue. Together, these studies expand our understanding of proton-sensitive ion channels by defining the functional properties of human OTOP3 and identifying extracellular elements regulating PKD1L3/TRPP3 activation. These findings provide insights into how extracellular acidification regulates ion channel function and establish a foundation for investigating proton-dependent gating and permeation mechanisms.
Recommended Citation
Da Costa Morais, Tiago, "MOLECULAR MECHANISMS OF PROTON-DEPENDENT GATING AND ION PERMEATION IN PROTON-SENSITIVE ION CHANNELS" (2026). Theses and Dissertations. 1140.
https://scholar.stjohns.edu/theses_dissertations/1140