title: A Ser/Thr protein kinase phosphorylates MA-ACS1 (Musa acuminata 1-aminocyclopropane-1-carboxylic acid synthase 1) during banana fruit ripening.
abstract: 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) catalyzes the rate-limiting step in ethylene biosynthesis during ripening. ACS isozymes are regulated both transcriptionally and post-translationally. However, in banana, an important climacteric fruit, little is known about post-translational regulation of ACS. Here, we report the post-translational modification of MA-ACS1 (Musa acuminata ACS1), a ripening inducible isozyme in the ACS family, which plays a key role in ethylene biosynthesis during banana fruit ripening. Immunoprecipitation analyses of phospholabeled protein extracts from banana fruit using affinity-purified anti-MA-ACS1 antibody have revealed phosphorylation of MA-ACS1, particularly in ripe fruit tissue. We have identified the induction of a 41-kDa protein kinase activity in pulp at the onset of ripening. The 41-kDa protein kinase has been identified as a putative protein kinase by MALDI-TOF/MS analysis. Biochemical analyses using partially purified protein kinase fraction from banana fruit have identified the protein kinase as a Ser/Thr family of protein kinase and its possible involvement in MA-ACS1 phosphorylation during ripening. In vitro phosphorylation analyses using synthetic peptides and site-directed mutagenized recombinant MA-ACS1 have revealed that serine 476 and 479 residues at the C-terminal region of MA-ACS1 are phosphorylated. Overall, this study provides important novel evidence for in vivo phosphorylation of MA-ACS1 at the molecular level as a possible mechanism of post-translational regulation of this key regulatory protein in ethylene signaling pathway in banana fruit during ripening.
authors.affiliation: Division of Plant Biology, Bose Institute, 93/1, Acharya Prafulla Chandra Road, Kolkata, 700 009, West Bengal, India. src.bose@gmail.com
authors.forename: Swarup Roy
authors.initials: SR
authors.lastname: Choudhury
authors.forename: Sujit
authors.initials: S
authors.lastname: Roy
authors.forename: Dibyendu N
authors.initials: DN
authors.lastname: Sengupta
mesh_terms: D000595:Amino Acid Sequence; D000598:Amino Acids, Cyclic / Q000378:metabolism; D000818:Animals; D005030:Ethylenes / Q000378:metabolism; D005638:Fruit / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D007074:Immunoglobulin G; D008190:Lyases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D028521:Musa / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D019606:Phosphoamino Acids / Q000032:analysis; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000598:Amino Acids, Cyclic; D005030:Ethylenes; D007074:Immunoglobulin G; D019606:Phosphoamino Acids; D010940:Plant Proteins; D011994:Recombinant Proteins; C023863:1-aminocyclopropane-1-carboxylic acid; C036216:ethylene; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase