Structural analysis of chloroplast tail‐anchored membrane protein recognition by ArsA1

• Published in: The Plant journal : for cell and molecular biology 2019-07, Vol.99 (1), p.128-143
• Main Authors: Lin, Tai‐Wen, Chen, Chi‐Chih, Wu, Shu‐Mei, Chang, Yu‐Ching, Li, Yi‐Chuan, Su, Yu‐Wang, Hsiao, Chwan‐Deng, Chang, Hsin‐Yang
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatase; Algae; ArsA1; ArsA2; Binding; Chlamydomonas reinhardtii; Chloroplasts; Chloroplasts - metabolism; Crystal structure; Domains; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Get3; Grooves; Helices; Homology; Membrane proteins; Membrane Proteins - metabolism; Membrane trafficking; Mitochondria; Nucleotides; Organelles; Plant cells; post‐translational pathway; Protein Binding; Protein Transport; Proteins; Recognition; Selectivity; Structural analysis; Substrates; tail‐anchored membrane protein; Translocation; TRC40; Yeast
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.14316

Summary In mammals and yeast, tail‐anchored (TA) membrane proteins destined for the post‐translational pathway are safely delivered to the endoplasmic reticulum (ER) membrane by a well‐known targeting factor, TRC40/Get3. In contrast, the underlying mechanism for translocation of TA proteins in plants remains obscure. How this unique eukaryotic membrane‐trafficking system correctly distinguishes different subsets of TA proteins destined for various organelles, including mitochondria, chloroplasts and the ER, is a key question of long standing. Here, we present crystal structures of algal ArsA1 (the Get3 homolog) in a distinct nucleotide‐free open state and bound to adenylyl‐imidodiphosphate. This approximately 80‐kDa protein possesses a monomeric architecture, with two ATPase domains in a single polypeptide chain. It is capable of binding chloroplast (TOC34 and TOC159) and mitochondrial (TOM7) TA proteins based on features of its transmembrane domain as well as the regions immediately before and after the transmembrane domain. Several helices located above the TA‐binding groove comprise the interlocking hook‐like motif implicated by mutational analyses in TA substrate recognition. Our data provide insights into the molecular basis of the highly specific selectivity of interactions of algal ArsA1 with the correct sets of TA substrates before membrane targeting in plant cells. Significance Statement The molecular and cellular mechanisms responsible for targeting tail‐anchored (TA) proteins in plant cells remain insufficiently understood, despite the likelihood that they play essential roles in metabolic regulation and responses to environmental stress, amongst other processes, in different membrane‐bound organelles during plant growth and development. Here, we propose a model of the TA pathway that is based on structural and biochemical data to explain how these diverse organelle‐targeting signals are appropriately recognized by a targeting factor(s) in plant cells.