A mouse Ig kappa domain of very unusual framework structure loses function when converted to the consensus

An Engineered Pathway for Production of Terminally Sialylated N-glycoproteins in the Periplasm of Escherichia coli

Terminally sialylated N-glycoproteins are of great interest in therapeutic applications. Due to the inability of prokaryotes to carry out this post-translational modification, they are currently predominantly produced in eukaryotic host cells. In this study, we report a synthetic pathway to produce a terminally sialylated N-glycoprotein in the periplasm of Escherichia coli, mimicking the sialylated moiety (Neu5Ac-α-2,6-Gal-β-1,4-GlcNAc-) of human glycans. A sialylated pentasaccharide, Neu5Ac-α-2,6-Gal-β-1,4-GlcNAc-β-1,3-Gal-β-1,3-GlcNAc-, was synthesized through the activity of co-expressed glycosyltransferases LsgCDEF from Haemophilus influenzae, Campylobacter jejuni NeuBCA enzymes, and Photobacterium leiognathi α-2,6-sialyltransferase in an engineered E. coli strain which produces CMP-Neu5Ac. C. jejuni oligosaccharyltransferase PglB was used to transfer the terminally sialylated glycan onto a glyco-recognition sequence in the tenth type III cell adhesion module of human fibronectin. Sialylation of the target protein was confirmed by lectin blotting and mass spectrometry. This proof-of-concept study demonstrates the successful production of terminally sialylated, homogeneous N-glycoproteins with α-2,6-linkages in the periplasm of E. coli and will facilitate the construction of E. coli strains capable of producing terminally sialylated N-glycoproteins in high yield.

Immunoassay protocol for quantitation of protein kinase activities

Quantitation of at least two orders of magnitude of kinase enzyme concentration is achieved with detection of less than 0.1 U/well of src kinase activity (Fig. 3). A comparison between a sequential protocol, in which biotinylated peptide substance is captured prior to incubation with the kinase enzyme, and a simultaneous protocol, in which peptide capture and the kinase reaction proceed concurrently, demonstrates that the simpler simultaneous protocol provides similar detection sensitivity. these have also been demonstrated with 0.1 microM peptide substrate in a protein kinase A assay.5 Quantitation of protein kinase activity with chemiluminescent detection has been demonstrated with several different protein kinases, including both tyrosine and serine/threonine kinases.5 An immunoassay format provides high sensitivity and can be performed under conditions that most closely mimic physiological substrate and ATP concentrations with chemiluminescent detection. This assay format is also automated easily for use in high-throughput screening.

Recognition of E. coli tryptophan synthase by single-chain Fv fragments: comparison of PCR-cloning variants with the parental antibodies

The use of a recombinant antibody fragment instead of a complete antibody, as a conformational probe for protein structure and folding studies, can be technically advantageous provided that the recombinant fragment and its parental antibody recognize the antigen through the same mechanism. Monoclonal antibodies mAb19 and mAb93 are directed against the TrpB2 subunit of Escherichia coli tryptophan synthase and they have been extensively used as conformational probes of this protein. DNA sequences coding for single-chain variable fragments (scFv) of mAb19 and mAb93 were cloned and assembled by reverse transcription of the mRNAs from hybridomas and PCR amplification. A specialized plasmid vector, pFBX, was constructed; it enabled to express the scFvs as hybrids with the maltose-binding protein (MalE) in E. coli, and to purify them by affinity chromatography on cross-linked amylose. Six independent clones were sequenced for each hybridoma. All of them had differences in their nucleotide and amino acid sequences. A competition ELISA and the BIAcore biosensor apparatus were used to compare the energetics and kinetics with which the parental antibodies and the hybrids bound TrpB2. The antigen binding properties of the hybrids were close to those of the parental antibodies and they were only weakly affected by the differences of sequence between the clones, with one exception. The stability of one of the hybrids and its antigen binding properties were strongly modified by a change of Gln6 into Glu, introduced into its VH domain by the PCR primers. Simple models of bimolecular interaction did not fully account for the kinetic profiles obtained with the parental antibodies and the hybrids, and this complexity suggested the existence of a conformational heterogeneity in these molecules.

Identification of framework residues in a secreted recombinant antibody fragment that control production level and localization in Escherichia coli

The monoclonal antibody 5T4, directed against a human tumor-associated antigen, was expressed as a secreted Fab superantigen fusion protein in Escherichia coli. The product is a putative agent for immunotherapy of non-small cell lung cancer. During fermentation, most of the fusion protein leaked out from the periplasm to the growth medium at a level of approximately 40 mg/liter. This level was notably low compared with similar products containing identical CH1, CL, and superantigen moieties, and the Fv framework was therefore engineered. Using hybrid molecules, the light chain was found to limit high expression levels. Substituting five residues in VL increased the level almost 15 times, exceeding 500 mg/liter in the growth medium. Here, the substitutions Phe-10 --> Ser, Thr-45 --> Lys, Thr-77 --> Ser, and Leu-78 --> Val were most powerful. In addition, replacing four VH residues diminished cell lysis during fermentation. Thereby the product was preferentially located in the periplasm instead of the growth medium, and the total yield was more than 700 mg/liter. All engineered products retained a high affinity for the tumor-associated antigen. It is suggested that at least some of the identified framework residues generally have to be replaced to obtain high level production of recombinant Fab products in E. coli.