Hyunju Cho1, Francesca Stanzione2, Amrita Oak3, Geun Hyang Kim4, Sindura Yerneni3, Ling Qi5, Amadeu K Sum6, Christina Chan7. 1. Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA; Department of Chemistry, California Institute of Technology, Pasadena, CA 91125, USA. Electronic address: hjcho@caltech.edu. 2. Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, CO 80401, USA; Institute of Medical Science-University of Aberdeen, Aberdeen AB25 2ZD, UK. 3. Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA. 4. Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105, USA. 5. Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105, USA; Division of Metabolism, Endocrinology & Diabetes, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48105, USA. 6. Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, CO 80401, USA. 7. Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA; Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA. Electronic address: krischan@egr.msu.edu.
Abstract
Activation of inositol-requiring enzyme (IRE1α) is an indispensable step in remedying the cellular stress associated with lipid perturbation in the endoplasmic reticulum (ER) membrane. IRE1α is a single-spanning ER transmembrane protein possessing both kinase and endonuclease functions, and its activation can be fully achieved through the dimerization and/or oligomerization process. How IRE1α senses membrane lipid saturation remains largely unresolved. Using both computational and experimental tools, we systematically investigated the dimerization process of the transmembrane domain (TMD) of IRE1α and found that, with help of the serine 450 residue, the conserved tryptophan 457 residue buttresses the core dimerization interface of IRE1α-TMD. BiFC (bimolecular fluorescence complementation) experiments revealed that mutation on these residues abolished the saturated fatty acid-induced dimerization in the ER membrane and subsequently inactivated IRE1α activity in vivo. Therefore, our results suggest that the structural elements of IRE1α-TMD serve as a key sensor that detects membrane aberrancy.
Activation of inositol-requiring enzyme (span>n class="Gene">IRE1α) is an indispensable step in remedying the cellular stress associated with lipid perturbation in the endoplasmic reticulum (ER) membrane. IRE1α is a single-spanning ER transmembrane protein possessing both kinase and endonuclease functions, and its activation can be fully achieved through the dimerization and/or oligomerization process. How IRE1α senses membrane lipid saturation remains largely unresolved. Using both computational and experimental tools, we systematically investigated the dimerization process of the transmembrane domain (TMD) of IRE1α and found that, with help of the serine 450 residue, the conserved tryptophan 457 residue buttresses the core dimerization interface of IRE1α-TMD. BiFC (bimolecular fluorescence complementation) experiments revealed that mutation on these residues abolished the saturated fatty acid-induced dimerization in the ER membrane and subsequently inactivated IRE1α activity in vivo. Therefore, our results suggest that the structural elements of IRE1α-TMD serve as a key sensor that detects membrane aberrancy.
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