Andrea Camattari

Carbon source dependent promoters in yeasts.

Budding yeasts are important expression hosts for the production of recombinant proteins.The choice of the right promoter is a crucial point for efficient gene expression, as most regulations take place at the transcriptional level. A wide and constantly increasing range of inducible, derepressed and constitutive promoters have been applied for gene expression in yeasts in the past; their different behaviours were a reflection of the different needs of individual processes.Within this review we summarize the majority of the large available set of carbon source dependent promoters for protein expression in yeasts, either induced or derepressed by the particular carbon source provided. We examined the most common derepressed promoters for Saccharomyces cerevisiae and other yeasts, and described carbon source inducible promoters and promoters induced by non-sugar carbon sources. A special focus is given to promoters that are activated as soon as glucose is depleted, since such promoters can be very effective and offer an uncomplicated and scalable cultivation procedure.

Screening for cytochrome P450 expression in Pichia pastoris whole cells by P450-carbon monoxide complex determination.

Cytochrome P450 (CYP) enzymes are useful biocatalysts for the pharmaceutical and biotechnological industries. A high‐throughput method for quantification of CYP expression in yeast is needed in order to fully exploit the yeast expression system. Carbon monoxide (CO) difference spectra of whole cells have been successfully used for the quantification of heterologous CYP expressed in Escherichia coli in the 96‐well format; however, very few researchers have shown whole‐cell CO difference spectra with yeast cells using 1‐cm path length. Spectral interference from the native hemoproteins often obscures the P450 peak, challenging functional CYP quantification in whole yeast cells. For the first time, we describe the high‐throughput determination of CO difference spectra using whole cells in the 96‐well format for the quantification of CYP genes expressed in Pichia pastoris. Very little interference from the hemoproteins of P. pastoris enabled CYP quantification even at relatively low expression levels. P. pastoris strains carrying a single copy or three copies of both hCPR and CYP2D6 integrated into the chromosomal DNA were used to establish the method in 96‐well format, allowing to detect quantities of CYP2D6 as low as 6 nmol gCDW–1 and 12 pmol per well. Finally, the established method was successfully demonstrated and used to screen P. pastoris clones expressing Candida CYP52A13.

Production of Recombinant Human Aldehyde Oxidase in Escherichia coli and Optimization of Its Application for the Preparative Synthesis of Oxidized Drug Metabolites

Recombinant human aldehyde oxidase (AO) was expressed in Escherichia coli. Different cell disruption methods and conditions of cell culture in shake flasks and bioreactors and of biotransformation on an analytical scale were tested to optimize the synthesis of oxidized AO drug metabolites. The volumetric productivity was increased 24‐fold by optimizing the cell culture conditions. The highest yield was achieved in a 25 L stirred tank bioreactor under non‐oxygen‐limited conditions and high lactose feed rate. Suspensions of highly concentrated and well‐aerated whole cells at neutral pH and relatively low temperatures led to the best conversion. The solvent for the substrate and the buffering agent for the biotransformation had an important effect. In a biotransformation with AO, 210 mg of famciclovir was converted to diacetyl penciclovir a yield of 82 %. The optimized protocol represents a viable method for the preparative synthesis of oxidized AO metabolites of drugs.

Methods for Efficient High-Throughput Screening of Protein Expression in Recombinant Pichia pastoris Strains

The methylotrophic yeast Pichia pastoris is becoming one of the favorite industrial workhorses for protein expression. Due to the widespread use of integration vectors, which generates significant clonal variability, screening methods allowing assaying hundreds of individual clones are of particular importance. Here we describe methods to detect and analyze protein expression, developed in a 96-well format for high-throughput screening of recombinant P. pastoris strains. The chapter covers essentially three common scenarios: (1) an enzymatic assay for proteins expressed in the cell cytoplasm, requiring cell lysis; (2) a whole-cell assay for a fungal cytochrome P450; and (3) a nonenzymatic assay for detection and quantification of tagged protein secreted into the supernatant.

Pichia pastoris mutants as host strains for efficient secretion of recombinant branched chain aminotransferase (BCAT).

Branched chain aminotransferase (BCAT) is one of the enzymatic tools of choice for the production of chiral amines or amino acids; especially, non-natural amino acids are of interest as building blocks for the pharmaceutical industry. The expression and subsequent secretion of BCAT counteracts limited cell permeability of target substrates and facilitates downstream processing. Since Pichia pastoris secretes a negligible amount of native proteins and was previously shown to efficiently secrete recombinant proteins, it was chosen as the expression host. We examined different promoters and glycosylation states and also engineered the host strain by disrupting genes encoding proteins related to cell wall assembly (Scw10, Cwp1) and glycosylation (Och1). Finally, we were able not only to increase the extracellular BCAT production, but also to achieve a more homogenous product in terms of glycosylation and identified a deletion strain, which counteracts typical cell clustering in the Δoch1 strain.