The cytoplasmic domain is essential for transport function of the integral membrane transport protein SLC4A11

Am J Physiol Cell Physiol. 2016 Jan 15;310(2):C161-74. doi: 10.1152/ajpcell.00246.2015. Epub 2015 Nov 18.


Large cytoplasmic domains (CD) are a common feature among integral membrane proteins. In virtually all cases, these CD have a function (e.g., binding cytoskeleton or regulatory factors) separate from that of the membrane domain (MD). Strong associations between CD and MD are rare. Here we studied SLC4A11, a membrane transport protein of corneal endothelial cells, the mutations of which cause genetic corneal blindness. SLC4A11 has a 41-kDa CD and a 57-kDa integral MD. One disease-causing mutation in the CD, R125H, manifests a catalytic defect, suggesting a role of the CD in transport function. Expressed in HEK-293 cells without the CD, MD-SLC4A11 is retained in the endoplasmic reticulum, indicating a folding defect. Replacement of CD-SLC4A11 with green fluorescent protein did not rescue MD-SLC4A11, suggesting some specific role of CD-SLC4A11. Homology modeling revealed that the structure of CD-SLC4A11 is similar to that of the Cl(-)/HCO3(-) exchange protein AE1 (SLC4A1) CD. Fusion to CD-AE1 partially rescued MD-SLC4A11 to the cell surface, suggesting that the structure of CD-AE1 is similar to that of CD-SLC4A11. The CD-AE1-MD-SLC4a11 chimera, however, had no functional activity. We conclude that CD-SLC4A11 has an indispensable role in the transport function of SLC4A11. CD-SLC4A11 forms insoluble precipitates when expressed in bacteria, suggesting that the domain cannot fold properly when expressed alone. Consistent with a strong association between CD-SLC4A11 and MD-SLC4A11, these domains specifically associate when coexpressed in HEK-293 cells. We conclude that SLC4A11 is a rare integral membrane protein in which the CD has strong associations with the integral MD, which contributes to membrane transport function.

Keywords: SLC4A11; corneal dystrophy; cytoplasmic domain; membrane domain; protein misfolding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anion Transport Proteins / chemistry*
  • Anion Transport Proteins / metabolism*
  • Antiporters / chemistry*
  • Antiporters / metabolism*
  • Bicarbonates / chemistry*
  • Bicarbonates / metabolism*
  • Biological Transport, Active / physiology
  • Cytoplasm / chemistry*
  • Cytoplasm / metabolism*
  • HEK293 Cells
  • Humans
  • Ion Channel Gating / physiology
  • Protein Structure, Tertiary
  • Structure-Activity Relationship


  • Anion Transport Proteins
  • Antiporters
  • Bicarbonates
  • SLC4A11 protein, human