title: Identification of thioredoxin h-reducible disulphides in proteomes by differential labelling of cysteines: insight into recognition and regulation of proteins in barley seeds by thioredoxin h.
abstract: Using thiol-specific fluorescence labelling, over 30 putative target proteins of thioredoxin h with diverse structures and functions have been identified in seeds of barley and other plants. To gain insight at the structural level into the specificity of target protein reduction by thioredoxin h, thioredoxin h-reducible disulphide bonds in individual target proteins are identified using a novel strategy based on differential alkylation of cysteine thiol groups by iodoacetamide and 4-vinylpyridine. This method enables the accessible cysteine side chains in the thiol form (carbamidomethylated) to be distinguished from those inaccessible or disulphide bound form (pyridylethylated) according to the mass difference in the peptide mass maps obtained by matrix-assistend laser desorption/ionisation-time of flight mass spectrometry. Using this approach, in vitro reduction of disulphides in recombinant barley alpha-amylase/subtilisin inhibitor (BASI) by barley thioredoxin h isoform 1 was analysed. Furthermore, the method was coupled with two-dimensional electrophoresis for convenient thioredoxin h-reducible disulphide identification in barley seed extracts without the need for protein purification or production of recombinant proteins. Mass shifts of 15 peptides, induced by treatment with thioredoxin h and differential alkylation, identified specific reduction of nine disulphides in BASI, four alpha-amylase/trypsin inhibitors and a protein of unknown function. Two specific disulphides, located structurally close to the alpha-amylase binding surfaces of BASI and alpha-amylase inhibitor BMAI-1 were demonstrated to be reduced to a particularly high extent. For the first time, specificity of thioredoxin h for particular disulphide bonds is demonstrated, providing a basis to study structural aspects of the recognition mechanism and regulation of target proteins.
authors.affiliation: Department of Chemistry, Carlsberg Laboratory, Copenhagen, Denmark.
authors.forename: Kenji
authors.initials: K
authors.lastname: Maeda
authors.forename: Christine
authors.initials: C
authors.lastname: Finnie
authors.forename: Birte
authors.initials: B
authors.lastname: Svensson
mesh_terms: D000485:Allergens / Q000378:metabolism; D000595:Amino Acid Sequence; D052179:Antigens, Plant; D003545:Cysteine / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D001467:Hordeum / Q000196:embryology / Q000378:metabolism*; D007460:Iodoacetamide; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010449:Peptide Mapping; D010940:Plant Proteins / Q000378:metabolism; D020543:Proteome / Q000378:metabolism*; D011725:Pyridines; D012639:Seeds / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013194:Staining and Labeling; D013438:Sulfhydryl Compounds / Q000378:metabolism; D054480:Thioredoxin h; D013879:Thioredoxins / Q000378:metabolism*; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000378:metabolism
chemical_list: D000485:Allergens; D052179:Antigens, Plant; D004220:Disulfides; D010940:Plant Proteins; D020543:Proteome; D011725:Pyridines; D013438:Sulfhydryl Compounds; D054480:Thioredoxin h; C092772:barley alpha-amylase-subtilisin inhibitor; C077622:IAM1 protein, Hordeum vulgare; D013879:Thioredoxins; D014360:Trypsin Inhibitor, Kunitz Soybean; C029351:4-vinylpyridine; D003545:Cysteine; D007460:Iodoacetamide