Laura Simmons

A GPI-linked protein that interacts with Ret to form a candidate neurturin receptor.

Glial-cell-line-derived neurotrophic factor (GDNF) and neurturin (NTN) are two structurally related, potent survival factors for sympathetic, sensory and central nervous system neurons. GDNF mediates its actions through a multicomponent receptor system composed of a ligand-binding glycosyl-phosphatidylinositol (GPI)-linked protein (designated GDNFR-α) and the transmembrane protein tyrosine kinase Ret. In contrast, the mechanism by which the NTN signal is transmitted is not well understood. Here we describe the identification and tissue distribution of a GPI-linked protein (designated NTNR-α) that is structurally related to GDNFR-α. We further demonstrate that NTNR-α binds NTN (Kd ∼ 10 pM) but not GDNF with high affinity; that GDNFR-α binds to GDNF but not NTN with high affinity; and that cellular responses to NTN require the presence of NTNR-α. Finally, we show that NTN, in the presence of NTNR-α, induces tyrosine-phosphorylation of Ret, and that NTN, NTNR-α and Ret form a physical complex on the cell surface. These findings identify Ret and NTNR-α as signalling and ligand-binding components, respectively, of a receptor for NTN and define a novel family of receptors for neurotrophic and differentiation factors composed of a shared transmembrane protein tyrosine kinase and a ligand-specific GPI-linked protein.

Expression of full-length immunoglobulins in Escherichia coli: rapid and efficient production of aglycosylated antibodies.

Many research and clinical applications require large quantities of full-length antibodies with long circulating half-lives, and production of these complex multi-subunit proteins has in the past been restricted to eukaryotic hosts. In this report, we demonstrate that efficient secretion of heavy and light chains in a favorable ratio leads to the high-level expression and assembly of full-length IgGs in the Escherichia coli periplasm. The technology described offers a rapid, generally applicable and potentially inexpensive method for the production of full-length therapeutic antibodies, as verified by the expression of several humanized IgGs. One E. coli-derived antibody in particular, anti-tissue factor IgG1, has been thoroughly evaluated and has all of the expected properties of an aglycosylated antibody, including tight binding to antigen and the neonatal receptor. As predicted, the protein lacks binding to C1q and the FcgammaRI receptor, making it an ideal candidate for research purposes and therapeutic indications where effector functions are either not required or are actually detrimental. In addition, a limited chimpanzee study suggests that the E. coli-derived IgG1 retains the long circulating half-life of mammalian cell-derived antibodies.

Capillary size exclusion chromatography with picogram sensitivity for analysis of monoclonal antibodies purified from harvested cell culture fluid

Size exclusion chromatography (SEC) is widely used in the characterization and quality control of therapeutic proteins to detect aggregates. Aggregation is a carefully monitored quality attribute from the earliest stages of clinical development owing to the possibility of eliciting an immunogenic response in the patient. During early stage molecule assessment for cell culture production, small-scale screening experiments are performed to permit rapid turn-around of results so as to not delay timelines. We report the development of a capillary SEC methodology for preliminary molecule assessment to support the evaluation of therapeutic candidates at an early stage of development. By making several key modifications to a commercially available liquid chromatography system, we demonstrate a platform process to perform capillary SEC with excellent precision, picogram sensitivity and good ruggedness. The limit of quantitation was determined to be approximately 15 pg; picogram sensitivity for SEC analysis of monoclonal antibodies had not been achieved prior to this work. In addition, we have developed a method to capture low levels of antibody (1 μg/mL) from harvested cell culture fluid (HCCF) for capillary SEC analysis. Up to 40% recovery efficiency was achieved using this micro-recovery method on 3 mL HCCF samples. Using early stage cell culture transient transfection samples, which typically have much lower titers than stable cell line samples, we demonstrate a consistent method for analyzing aggregates in low protein concentration HCCF samples for molecule assessment and early stage candidate screening.

Slashing the timelines: Opting to generate high-titer clonal lines faster via viability-based single cell sorting.

Chinese hamster ovary (CHO) cell line development (CLD) is a long and laborious process, which requires up to 5 − 6 months in order to generate and bank CHO lines capable of stably expressing therapeutic molecules. Additionally, single cell cloning of these production lines is also necessary to confirm clonality of the production lines. Here we introduce the utilization of viability staining dye in combination with flow cytometer to isolate high titer clones from a pool of selected cells and single cell deposit them into the wells of culture plates. Our data suggests that a stringent selection procedure along with viability dye staining and flow cytometry‐based sorting can be used to isolate high expressing clones with titers comparable to that of traditional CLD methods. This approach not only requires less labor and consumables, but it also shortens CLD timelines by at least 3 weeks. Furthermore, single cell deposition of selected cells by a flow sorter can be regarded as an additional clonality assurance factor that in combination with Day 0 imaging can ensure clonality of the production lines.

Nucleotide sequence selection for increased expression of heterologous genes in Escherichia coli

Abstract We have developed a method for selecting nucleotide sequences at the beginning of heterologous genes that leads to their high-level expression in Escherichia coli . This part of the coding sequence can have a large influence on translational initiation, presumably through its ability to affect mRNA secondary structure around the Shine-Dalgarno sequence and the initiation codon. Our method involves the construction of a codon bank at the beginning of a gene of interest that retains all of the correct amino acids for that protein. A simple selection procedure is then used to enrich for those sequences from the bank that lead to high levels of translation. The selection procedure is based on the use of a translationally coupled tetracycline resistance gene. Bacteriocidal permeability increasing protein (BPI) was chosen as an example, since the use of the original cDNA sequence leads to poor expression. After the construction of the codon bank at the beginning of the BPI coding sequence and subsequent selection, several sets of nucleotide sequences that resulted in high levels of expression were found.

Correction: A GPI-linked protein that interacts with Retto form a candidate neurturin receptor

This corrects the article DOI: 10.1038/42722