At-Line Reversed Phase Liquid Chromatography for In-Process Monitoring of Inclusion Body Solubilization

Comprehensive evaluation of recombinant lactate dehydrogenase production from inclusion bodies

A broad application spectrum ranging from clinical diagnostics to biosensors in a variety of sectors, makes the enzyme Lactate dehydrogenase (LDH) highly interesting for recombinant protein production. Expression of recombinant LDH is currently mainly carried out in uncontrolled shake-flask cultivations leading to protein that is mostly produced in its soluble form, however in rather low yields. Inclusion body (IB) processes have gathered a lot of attention due to several benefits like increased space-time yields and high purity of the target product. Thus, to investigate the suitability of this processing strategy for ldhL1 production, a fed-batch fermentation steering the production of IBs rather than soluble product formation was developed. It was shown that the space-time-yield of the fermentation could be increased almost 3-fold by increasing qs to 0.25 g g-1 h-1 which corresponds to 21% of qs,max, and keeping the temperature at 37°C after induction. Solubilization and refolding unit operations were developed to regain full bioactivity of the ldhL1. The systematic approach in screening for solubilization and refolding conditions revealed buffer compositions and processing strategies that ultimately resulted in 50% product recovery in the refolding step, revealing major optimization potential in the downstream processing chain. The recovered ldhL1 showed an optimal activity at pH 5.5 and 30∘C with a high catalytic activity and KM values of 0.46 mM and 0.18 mM for pyruvate and NADH, respectively. These features, show that the here produced LDH is a valuable source for various commercial applications, especially considering low pH-environments.

High Pressure Homogenization for Inclusion Body Isolation

High pressure homogenization (HPH) is a commonly used method for cell lysis of Escherichia coli in order to release intracellularly produced recombinant proteins. For misfolded proteins in E. coli, focus is often put on the development of a suitable solubilization and refolding protocol. However, HPH can be a critical unit operation influencing inclusion body (IB) quality and, subsequently, refolding yields. Here, a protocol for homogenization and IB washing is presented in combination with analytical methods suitable to evaluate these unit operations. The protocol is based on a multivariate approach to identify suitable conditions during HPH. Furthermore, the described workflow is easily scalable and can, therefore, also be used if fixed homogenization conditions are already established.

Unit Operation-Spanning Investigation of the Redox System

Cytoplasmic expression of recombinant proteins requiring disulfide bridges in Escherichia coli usually leads to the formation of insoluble inclusion bodies (IBs). The reason for this phenomenon is found in the reducing environment of the cytoplasm, preventing the formation of disulfide bridges and therefore resulting in inactive protein aggregates. However, IBs can be refolded in vitro to obtain the protein in its active conformation. In order to correctly form the required disulfide bridges, cystines are fully reduced during solubilization and, with the help of an oxidizing agent, the native disulfide bridges are formed during the refolding step. Here, a protocol to identify suitable redox conditions for solubilization and refolding is presented. For this purpose, a multivariate approach spanning the unit operations solubilization and refolding is used.

QCL-IR Spectroscopy for In-Line Monitoring of Proteins from Preparative Ion-Exchange Chromatography

In this study, an external cavity-quantum cascade laser-based mid-infrared (IR) spectrometer was applied for in-line monitoring of proteins from preparative ion-exchange chromatography. The large optical path length of 25 μm allowed for robust spectra acquisition in the broad tuning range between 1350 and 1750 cm^–1, covering the most important spectral region for protein secondary structure determination. A significant challenge was caused by the overlapping mid-IR bands of proteins and changes in the background absorption of water due to the NaCl gradient. Implementation of advanced background compensation strategies resulted in high-quality protein spectra in three different model case studies. In Case I, a reference blank run was directly subtracted from a sample run with the same NaCl gradient. Case II and III included sample runs with different gradient profiles than the one from the reference run. Here, a novel compensation approach based on a reference spectra matrix was introduced, where the signal from the conductivity detector was employed for correlating suitable reference spectra for correction of the sample run spectra. With this method, a single blank run was sufficient to correct various gradient profiles. The obtained IR spectra of hemoglobin and β-lactoglobulin were compared to off-line reference measurements, showing excellent agreement for all case studies. Moreover, the concentration values obtained from the mid-IR spectrometer agreed well with conventional UV detectors and high-performance liquid chromatography off-line measurements. LC–QCL–IR coupling thus holds high potential for replacing laborious and time-consuming off-line methods for protein monitoring in complex downstream processes.