Disease‐Causing Mutations Shift the pK of the pH‐Sensitive H+‐Conductor Slc4a11

Abstract

SLC4A11 is a H+‐conducting membrane protein that is sensitive to changes in both intracellular and extracellular pH. It is expressed in corneal endothelial cells (CECs) where it functions alongside other acid/base transporters such as MCT1 and NBCe1. These proteins function to maintain the osmotic balance and clarity of the cornea. Mutations in SLC4A11 cause congenital hereditary endothelial dystrophy (CHED) and Fuchs’ endothelial corneal dystrophy (FECD). Signs of these corneal dystrophies include loss of normal CEC morphology and corneal edema. Previously—using the Xenopus oocyte expression system, two‐electrode voltage clamp circuitry (to monitor conductance), and H+‐selective microelectrodes (to monitor intracellular pH)—we determined that the intracellular pK of wild‐type (WT) mouse Slc4a11 activity is 7.15 ± 0.04 (n=13, SD, pHe=8.5). In this study we use the same experimental setup to explore whether disease‐causing mutations can affect the intracellular‐pH dependence (pK) of Slc4a11.We chose FECD mutation E399K and CHED mutations T401K and R804H for comparison to WT due to the loss or gain of a titratable residue. We find that Slc4a11‐‘E399K’ exhibits a pK value of 7.02 ± 0.03 (n = 6, SD) and that Slc4a11‐‘T401K’ exhibits a pK value of 7.09 ± 0.03 (n = 6, SD); both significantly acid‐shifted compared to WT. On the other hand, ‘R804H’‐Slc4a11 exhibits a significantly alkali‐shifted pK value of 7.29 ± 0.04 (n = 6, SD) [Statistics are the result of two‐tailed unpaired t‐tests with Bonferroni correction].Thus we describe three disease‐causing mutations that cause a shift in the intracellular pK value of Slc4a11. If the pH‐dependence of the H+ conductance mediated by Slc4a11 is critical to the physiological role of Slc4a11, these shifts in pK could contribute towards the etiology of corneal dystrophy.Support or Funding InformationThis work was supported by NIH R01‐EY028580 to MDP.