Alternative oxidase (AOX) constitutes a small family of proteins in Citrus clementina and Citrus sinensis L. Osb

• Published in: PloS one Vol. 12; no. 5; p. e0176878
• Main Authors: Araújo Castro, Jacqueline, Gomes Ferreira, Monique Drielle, Santana Silva, Raner José, Andrade, Bruno Silva, Micheli, Fabienne
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.05.2017; Public Library of Science (PLoS)
• Subjects: Adenosine triphosphate; Alignment; Alternative oxidase; Amino Acid Sequence; Amino acids; Biochemistry; Bioenergetics; Biology and Life Sciences; Boron; Botany; Breeding; Calcium; Callus; Chemical synthesis; Chilling; Citrus - enzymology; Citrus - genetics; Citrus fruits; Citrus sinensis; Cladistic analysis; Computer programs; Conserved Sequence; Construction; Cooling; Coverage; Cyanides; Cytochrome; Drought; Energy conservation; Environmental assessment; Environmental factors; Exons; Fecundity; Fruits; Fungi; Gene expression; Gene Expression Regulation, Plant - physiology; Gene families; Genes; Genetic aspects; Genomes; Homeostasis; Homology; Hydrogen peroxide; Hydrophobic and Hydrophilic Interactions; Infections; Invertebrates; Iron; Light effects; Metabolism; Mitochondria - metabolism; Mitochondrial Proteins - genetics; Mitochondrial Proteins - metabolism; Molecular biology; Molecular docking; Molecular Docking Simulation; Nucleotide sequence; Oranges; Oxidoreductases - genetics; Oxidoreductases - metabolism; Oxygen; Phylogenetics; Phylogeny; Physiology; Plant breeding; Plant mitochondria; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Structures - enzymology; Plant Structures - genetics; Promoter Regions, Genetic; Protein Processing, Post-Translational; Protein Structure, Secondary; Proteins; Protozoa; Research and Analysis Methods; Residues; Respiration; Sequence Homology, Amino Acid; Software; Species Specificity; Statistical analysis; Structural analysis; Surgical implants; Tangerines; Three dimensional models; Transportation; Ubiquinone - metabolism; Brazil
• DOI: 10.1371/journal.pone.0176878
• ISSN: 1932-6203

The alternative oxidase (AOX) protein is present in plants, fungi, protozoa and some invertebrates. It is involved in the mitochondrial respiratory chain, providing an alternative route for the transport of electrons, leading to the reduction of oxygen to form water. The present study aimed to characterize the family of AOX genes in mandarin (Citrus clementina) and sweet orange (Citrus sinensis) at nucleotide and protein levels, including promoter analysis, phylogenetic analysis and C. sinensis gene expression. This study also aimed to do the homology modeling of one AOX isoform (CcAOXd). Moreover, the molecular docking of the CcAOXd protein with the ubiquinone (UQ) was performed. Four AOX genes were identified in each citrus species. These genes have an open reading frame (ORF) ranging from 852 bp to 1150 bp and a number of exons ranging from 4 to 9. The 1500 bp-upstream region of each AOX gene contained regulatory cis-elements related to internal and external response factors. CsAOX genes showed a differential expression in citrus tissues. All AOX proteins were predicted to be located in mitochondria. They contained the conserved motifs LET, NERMHL, LEEEA and RADE-H as well as several putative post-translational modification sites. The CcAOXd protein was modeled by homology to the AOX of Trypanosona brucei (45% of identity). The 3-D structure of CcAOXd showed the presence of two hydrophobic helices that could be involved in the anchoring of the protein in the inner mitochondrial membrane. The active site of the protein is located in a hydrophobic environment deep inside the AOX structure and contains a diiron center. The molecular docking of CcAOXd with UQ showed that the binding site is a recessed pocket formed by the helices and submerged in the membrane. These data are important for future functional studies of citrus AOX genes and/or proteins, as well as for biotechnological approaches leading to AOX inhibition using UQ homologs.