Article | Published:

A novel tripartite motif involved in aquaporin topogenesis, monomer folding and tetramerization

Nature Structural & Molecular Biology volume 14, pages 762769 (2007) | Download Citation

Abstract

Aquaporin (AQP) folding in the endoplasmic reticulum is characterized by two distinct pathways of membrane insertion that arise from divergent residues within the second transmembrane segment. We now show that in AQP1 these residues (Asn49 and Lys51) interact with Asp185 at the C terminus of TM5 to form a polar, quaternary structural motif that influences multiple stages of folding. Asn49 and Asp185 form an intramolecular hydrogen bond needed for proper helical packing, monomer formation and function. In contrast, Lys51 interacts with Asp185 on an adjacent monomer to stabilize the AQP1 tetramer. Although these residues are unique to AQP1, they share a highly conserved architecture whose functional properties can be transferred to other family members. These findings suggest a general mechanism by which evolutionary divergence of membrane proteins can confer new functional properties via alternative folding pathways that give rise to a common final structure.

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Acknowledgements

The authors thank F. Larabee for his expert technical assistance, and L. Musil, D. Koop, C. Enns and S.-L. Shyng and members of the Skach laboratory for their valuable advice and comments. This work was supported by US National Institutes of Health grants GM53457 (W.R.S.), DK51818 (W.R.S.) and T32HL07781 (T.M.B.).

Author information

Author notes

    • Teresa M Buck

    Present address: University of Pittsburgh, Department of Biological Sciences, 274 Crawford Hall, Pittsburgh, Pennsylvania 15260, USA.

Affiliations

  1. Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, 3181 SW Sam Jackson Park Rd., Portland, Oregon 97239, USA.

    • Teresa M Buck
    • , Justin Wagner
    • , Steven Grund
    •  & William R Skach
  2. Division of Pulmonary and Critical Care, Oregon Health & Sciences University, 3181 SW Sam Jackson Park Rd., Portland, Oregon 97239, USA.

    • Steven Grund

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Contributions

T.M.B. generated cDNA constructs, performed protease and coimmunoprecipitation experiments, sucrose-gradient analyses and most oocyte functional studies. J.W. contributed to cDNA cloning and performed functional oocyte studies. S.G. performed oocyte expression and coimmunoprecipitation studies. W.R.S. directed the study, designed experiments, wrote the manuscript (with T.M.B.) and analyzed AQP structures.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to William R Skach.

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DOI

https://doi.org/10.1038/nsmb1275

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