| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 107 === Eukaryotic organisms are featured by cellular compartmentalization with variety of specific membrane-enclosed organelles. The proper function of these organelles requires complex molecular machineries for accurate protein recognition and effective sorting of proteins from the cytosol to their functional location. Tail-anchored membrane (TA) proteins are a subset of membrane proteins characterized by a single hydrophobic alpha helix located at the most C-terminal region. With this unique topology, a specialized post-translational pathway called GET pathway is required to mediate the effective targeting of TA proteins to ER membrane. In the past few years, GET pathway was extensively studied and well established in mammalian and yeast. However, it remains largely unclear about the molecular machines responsible for the selective recognition of TA proteins in plant cells particularly for the chloroplast TA proteins. Recent study had demonstrated that green algae CrArsA1 can selectively mediate the insertion of TA protein into the chloroplast outer envelope but not for ER TA protein. To understand the mechanism underlying its specificity, we crystallized and solved CrArsA1 protein structure in apo and AMPPNP-bound form. Both structures reveal an open conformation with an unusual compact interlocking hook-like subdomain next to the TA protein binding site. We found that CrArsA1 with mutation within this subdomain significantly lose its selectivity and can recognize to both chloroplast and ER TA proteins. This indicates that CrArsA1 adapts a novel compact substructure to discriminate chloroplast TA protein from other TA proteins.
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