title: Structure, Diversity, and Evolution of a New Family of Soluble Carotenoid-Binding Proteins in Cyanobacteria.
abstract: Using a phylogenomic approach, we have identified and subclassified a new family of carotenoid-binding proteins. These proteins have sequence homology to the N-terminal domain (NTD) of the Orange Carotenoid Protein (OCP), and are referred to as Helical Carotenoid Proteins (HCPs). These proteins comprise at least nine distinct clades and are found in diverse organisms, frequently as multiple paralogs representing the distinct clades. These seem to be out-paralogs maintained from ancient duplications associated with subfunctionalization. All of the HCPs share conservation of the residues for carotenoid binding, and we confirm that carotenoid binding is a fundamental property of HCPs. We solved two crystal structures of the Nostoc sp. PCC 7120 HCP1 protein, each binding a different carotenoid, suggesting that the proteins flexibly bind a range of carotenoids. Based on a comprehensive phylogenetic analysis, we propose that one of the HCP subtypes is likely the evolutionary ancestor of the NTD of the OCP, which arose following a domain fusion event. However, we predict that the majority of HCPs have functions distinct from the NTD of the OCP. Our results demonstrate that the HCPs are a new family of functionally diverse carotenoid-binding proteins found among ecophysiologically diverse cyanobacteria.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Melnicki
authors.affiliation: MSU-DOE Plant Research Laboratory, Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Leverenz
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; MSU-DOE Plant Research Laboratory, Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Markus
authors.initials: M
authors.lastname: Sutter
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France; Commissariat à l'Energie Atomique (CEA), Institut de Biologie et Technologies de Saclay (iBiTec-S), 91191 Gif-sur-Yvette, France.
authors.forename: Rocío
authors.initials: R
authors.lastname: López-Igual
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France; Commissariat à l'Energie Atomique (CEA), Institut de Biologie et Technologies de Saclay (iBiTec-S), 91191 Gif-sur-Yvette, France.
authors.forename: Adjélé
authors.initials: A
authors.lastname: Wilson
authors.affiliation: MSU-DOE Plant Research Laboratory, Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Emily G
authors.initials: EG
authors.lastname: Pawlowski
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, 78026 Versailles, France.
authors.forename: François
authors.initials: F
authors.lastname: Perreau
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France; Commissariat à l'Energie Atomique (CEA), Institut de Biologie et Technologies de Saclay (iBiTec-S), 91191 Gif-sur-Yvette, France.
authors.forename: Diana
authors.initials: D
authors.lastname: Kirilovsky
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; MSU-DOE Plant Research Laboratory, Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA. Electronic address: ckerfeld@lbl.gov.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Kerfeld
mesh_terms: D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D010802:Phylogeny
chemical_list: D001426:Bacterial Proteins; D002338:Carotenoids
keywords: carotenoids; cyanobacteria; molecular evolution; photoprotection; phylogenomics; protein structure