Production and Characterization of Monoclonal Antibodies against Aspartate Aminotransferase-P(2) from Lupin Root Nodules

A novel peptide tag for detection and purification of recombinant expressed proteins

Peptide tags have proven useful for the detection and purification of recombinant proteins. However cross reactions of antibodies raised to the tag are frequently observed due to the presence of host proteins containing all or parts of the tag. In this report we have identified a unique viral peptide sequence, R-tag, that by blast searches is absent from the commonly expression hosts Arabidopsis thaliana, Escherichia coli, Pichia pastoris and mouse myeloma cell NSO. We have prepared monoclonal antibodies to this peptide and confirmed the absence of this peptide sequence from the above genomes by Western blotting. We have also modified protein expression vectors to incorporate this sequence as a fusion tag in expressed proteins and shown its use to successfully purify recombinant proteins by immunoaffinity procedures.

Characterization of aspartate aminotransferase isoenzymes from leaves of Lupinus albus L. cv Estoril

Two aspartate aminotransferase (EC 2.6.1.1) isoenzymes (AAT-1 and AAT-2) from Lupinus albus L. cv Estoril were separated, purified, and characterized. The molecular weight, pI value, optimum pH, optimum temperature, and thermodynamic parameters for thermal inactivation of both isoenzymes were obtained. Studies of the kinetic mechanism, and the kinetics of product inhibition and high substrate concentration inhibition, were performed. The effect of some divalent ions and irreversible inhibitors on both AAT isoenzymes was also studied. Native PAGE showed a higher molecular weight for AAT-2 compared with AAT-1. AAT-1 appears to be more anionic than AAT- 2, which was suggested by the anion exchange chromatography. SDS-PAGE showed a similar sub-unit molecular weight for both isoenzymes. The optimum pH (between 8.0 and 9.0) and temperature (60-65 degrees C) were similar for both isoenzymes. In the temperature range of 45-65 degrees C, AAT-2 has higher thermostability than AAT-1. Both isoenzymes showed a high affinity for keto-acid substrates, as well as a higher affinity to aspartate than glutamate. Manganese ions induced an increase in both AAT isoenzymes activities, but no cooperative effect was detected. Among the inhibitors tested, hydroxylamine affected both isoenzymes activity by an irreversible inhibition mechanism.

A system for tissue-specific copper-controllable gene expression in transgenic plants: nodule-specific antisense of aspartate aminotransferase-P2

A vector system, based on copper controllable gene expression, has been developed to give control over place as well as time of expression of an introduced gene. This system consists of two elements: (1) the yeast ace1 gene encoding a metallo-regulatory transcription factor, ACE1, under control of either an organ-specific or a constitutive promoter; and (2) a gene of interest under control of a chimaeric promoter consisting of the 46 bp TATA fragment of the CaMV 35S RNA promoter linked to four repeats of the ACE1 binding site. The functioning of the system in an organ-specific manner was tested in nodulated Lotus corniculatus plants which consisted of non-transformed shoots plus transformed hairy root tissue 'wild-type tops/transgenic roots'. After addition of copper ions to the plant nutrient solution, beta-glucuronidase (GUS) expression was visualized either specifically in nodules or in both roots and nodules when the ace1 gene was placed under control of the nod45 promoter or the CaMV 35S RNA promoter, respectively. The nodule-specific system was used to express antisense constructs of aspartate aminotransferase-P2 in transgenic Lotus corniculatus plants. When expression was induced by the addition of copper ions to the plant nutrient solution aspartate aminotransferase-P2 activity declined dramatically, and a decrease of up to 90% was observed in nodule asparagine concentration.

Cloning and characterization of a cDNA encoding aspartate aminotransferase-P1 from Lupinus angustifolius root tips

A root tip cDNA library, constructed in the lambda Zap II expression vector, was immunoscreened with a monoclonal antibody raised against aspartate aminotransferase-P1 from Lupinus angustifolius L. var Uniharvest. One 1452-base pair clone was isolated. The encoded protein sequence had high homology to both plant and animal aspartate aminotransferase sequences. The clone was converted to the phagemid form and expressed in Escherichia coli. The expressed protein was enzymically active and could be immunocomplexed with aspartate aminotransferase-P1-specific antibodies. The complete aspartate aminotransferase-P1 cDNA was cloned into the yeast expression vector pEMBL-yex4 and transformed into Saccharomyces cerevisiae strain BRSCS6, which possesses a mutated aspartate aminotransferase gene (the asp5 mutation). Complementation of the mutation was achieved using this construct.

Production and Characterization of Monoclonal Antibodies against Aspartate Aminotransferase-P1 from Lupin Root Nodules

Six hybridoma clones were obtained that secreted monoclonal antibodies against the aspartate aminotransferase-P1 (AAT-P1) isoenzyme from root nodules of Lupinus angustifolius [L.] cv Uniharvest. This enzyme is found constitutively in the plant cytosol fraction. The monoclonal antibodies produced were all of the immunoglobulin G1 class, recognized two distinct epitopes on the protein, and represented the major paratopes found in the immunoglobulin fraction of sera taken from mice and rabbits immunized with the pure AAT-P1 protein. One of these epitopes was unique to lupin nodule AAT-P1. The other epitope was shown to be present on enzyme from lupin bean, white clover and tobacco leaves, lupin roots and nodules, and potato tubers. Both epitopes were recognized by the appropriate monoclonal antibodies in both their native and denatured forms. None of the monoclonal antibodies produced reacted with Rhizobium lupini NZP2257, Escherichia coli extracts, or with the inducible aspartate aminotransferase-P2 (AAT-P2) isoform also found in root nodules. A sandwich enzyme-linked immunosorbent assay utilizing two monoclonal antibodies recognizing the two distinct epitopes was developed and was capable of quantitating AAT-P1 in plant extracts. The limit of detection of AAT-P1 was less than 15 pg/mL and AAT-P1 protein could be quantified in the range 80 to 1000 pg/mL. Using this assay, AAT-P1 protein was shown to remain relatively constant during nodule development. Use of an AAT-P2-specific monoclonal antibody that inhibits the enzyme activity of this isoform enabled the direct determination of AAT-P1 enzyme activity in nodule extracts. Using these assays, specific activities of the individual isoforms were calculated; that of the AAT-P1 isoform was shown to be 7.5-fold higher than that of the AAT-P2 isoform.

Production of monoclonal antibodies recognising different epitopes present on insulin-like growth factor 1

Monoclonal antibodies (MAbs) were generated against recombinant human insulin-like growth factor 1 (IGF-1) by fusion of NS-1 myeloma cells with spleen cells from BALB/c X DBA mice immunised with recombinant IGF-1 and synthetic peptide sequences derived from the published amino acid sequence of IGF-1. MAbs were produced that recognised four distinct epitopes including two defined segments of the C and D domains. All MAbs were IgM mouse immunoglobulins. These results indicate the feasibility of producing MAbs to highly conserved proteins.

Monoclonal antibodies against urease from Canavalia ensiformis

Monoclonal antibodies against purified urease (EC 3.5.1.5) from Canavalia ensiformis were raised by hybridoma technology using Sp2/0 myeloma cells as a fusion partner. All culture wells exhibited hybrid growth and 25% of these (ie 45 culture wells) contained anti-urease activity. Two positive hybrid cells were cloned twice by the limiting dilution method and three hybridoma clones (B6F, C4F and B18) secreting monoclonal antibodies were selected at random for purification and characterisation purposes. All three cell lines secreted monoclonal antibodies of IgM class which were purified by gel filtration chromatography on Sephacryl S-200 column with a final recovery of 85% and a purification factor of about 18. The purified preparations were apparently homogeneous on native PAGE running with a M(r) of 920,000 Da. mAbs were highly specific for jack bean urease as determined by Western blotting. The affinity constants (K) for these mAbs ranged from 10(8) to 10(9) l mol-1. mAb B6F inhibited about 65% of urease activity whereas C4F and B18 stimulated the enzyme activity slightly by 20%. The presence of 2-mercaptoethanol in incubation mixtures protected urease from inactivation by B6F. Urease inactivation by B6F could be reversed by addition of 2-mercaptoethanol which reactivated most of the partially inactive enzyme. Gel filtration chromatography of purified urease exhibited two protein peaks with M(r) values of 290,000 and 90,000 Da which revealed antibody activity. This result suggests that the mAb B6F recognizes the trimeric as well as the monomeric forms of urease.