title: The N-terminal Part of Arabidopsis thaliana Starch Synthase 4 Determines the Localization and Activity of the Enzyme.
abstract: Starch synthase 4 (SS4) plays a specific role in starch synthesis because it controls the number of starch granules synthesized in the chloroplast and is involved in the initiation of the starch granule. We showed previously that SS4 interacts with fibrillins 1 and is associated with plastoglobules, suborganelle compartments physically attached to the thylakoid membrane in chloroplasts. Both SS4 localization and its interaction with fibrillins 1 were mediated by the N-terminal part of SS4. Here we show that the coiled-coil region within the N-terminal portion of SS4 is involved in both processes. Elimination of this region prevents SS4 from binding to fibrillins 1 and alters SS4 localization in the chloroplast. We also show that SS4 forms dimers, which depends on a region located between the coiled-coil region and the glycosyltransferase domain of SS4. This region is highly conserved between all SS4 enzymes sequenced to date. We show that the dimerization seems to be necessary for the activity of the enzyme. Both dimerization and the functionality of the coiled-coil region are conserved among SS4 proteins from phylogenetically distant species, such as Arabidopsis and Brachypodium This finding suggests that the mechanism of action of SS4 is conserved among different plant species.
authors.affiliation: From the Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, University of Sevilla, Avenida Américo Vespucio 49, 41092 Sevilla, Spain.
authors.forename: Sandy
authors.initials: S
authors.lastname: Raynaud
authors.affiliation: From the Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, University of Sevilla, Avenida Américo Vespucio 49, 41092 Sevilla, Spain.
authors.forename: Paula
authors.initials: P
authors.lastname: Ragel
authors.affiliation: From the Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, University of Sevilla, Avenida Américo Vespucio 49, 41092 Sevilla, Spain.
authors.forename: Tomás
authors.initials: T
authors.lastname: Rojas
authors.affiliation: From the Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, University of Sevilla, Avenida Américo Vespucio 49, 41092 Sevilla, Spain angel.merida@csic.es.
authors.forename: Ángel
authors.initials: Á
authors.lastname: Mérida
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D058431:Brachypodium / Q000201:enzymology / Q000235:genetics; D017124:Conserved Sequence; D000071837:Fibrillins / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D013213:Starch / Q000096:biosynthesis; D013214:Starch Synthase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000201:enzymology
chemical_list: D029681:Arabidopsis Proteins; D000071837:Fibrillins; D010446:Peptide Fragments; D010940:Plant Proteins; D013213:Starch; D013214:Starch Synthase; C520418:starch synthase IV, Arabidopsis
keywords: Arabidopsis; carbohydrate biosynthesis; chloroplast; plant biochemistry; protein-protein interaction; starch initiation; starch synthase