Degradation of recombinant proteins by Chinese hamster ovary host cell proteases is prevented by matriptase-1 knockout.

An increasing number of nonantibody format proteins are entering clinical development. However, one of the major hurdles for the production of nonantibody glycoproteins is host cell-related proteolytic degradation, which can drastically impact developability and timelines of pipeline projects. Chinese hamster ovary (CHO) cells are the preferred production host for recombinant therapeutic proteins. Using protease inhibitors, transcriptomics, and genetic knockdowns, we have identified, out of the >700 known proteases in rodents, matriptase-1 as the major protease involved in the degradation of recombinant proteins expressed in CHO-K1 cells. Subsequently, matriptase-1 was deleted in CHO-K1 cells using "transcription activator-like effector nucleases" (TALENs) as well as zinc-finger nucleases (ZFNs). This resulted in a superior CHO-K1 matriptase (KO) cell line with strongly reduced or no proteolytic degradation activity toward a panel of recombinantly expressed proteins. The matriptase KO cell line was evaluated in spike-in experiments and showed little or no degradation of proteins incubated in culture supernatant derived from the KO cells. This effect was confirmed when the same proteins were recombinantly expressed in the KO cell line. In summary, the combination of novel cell line engineering tools, next-generation sequencing screening methods, and the recently published Chinese hamster genome has enabled the development of this novel matriptase KO CHO cell line capable of improving expression yields of intact therapeutic proteins.

Enabling low cost biopharmaceuticals: high level interferon alpha-2b production in Trichoderma reesei.

BACKGROUND: The filamentous fungus Trichoderma reesei has tremendous capability to secrete over 100 g/L of proteins and therefore it would make an excellent host system for production of high levels of therapeutic proteins at low cost. We have developed T. reesei strains suitable for production of therapeutic proteins by reducing the secreted protease activity. Protease activity has been the major hindrance to achieving high production levels. We have constructed a series of interferon alpha-2b (IFNα-2b) production strains with 9 protease deletions to gain knowledge for further strain development. RESULTS: We have identified two protease deletions that dramatically improved the production levels. Deletion of the subtilisin protease slp7 and the metalloprotease amp2 has enabled production levels of IFNα-2b up to 2.1 and 2.4 g/L, respectively. With addition of soybean trypsin protease inhibitor the level of production improved to 4.5 g/L, with an additional 1.8 g/L still bound to the secretion carrier protein. CONCLUSIONS: High levels of IFNα-2b were produced using T. reesei strains with reduced protease secretion. Further strain development can be done to improve the production system by reducing protease activity and improving carrier protein cleavage.

In vivo protein crystallization in combination with highly brilliant radiation sources offers novel opportunities for the structural analysis of post-translationally modified eukaryotic proteins.

During the last decade, the number of three-dimensional structures solved by X-ray crystallography has increased dramatically. By 2014, it had crossed the landmark of 100 000 biomolecular structures deposited in the Protein Data Bank. This tremendous increase in successfully crystallized proteins is primarily owing to improvements in cloning strategies, the automation of the crystallization process and new innovative approaches to monitor crystallization. However, these improvements are mainly restricted to soluble proteins, while the crystallization and structural analysis of membrane proteins or proteins that undergo major post-translational modifications remains challenging. In addition, the need for relatively large crystals for conventional X-ray crystallography usually prevents the analysis of dynamic processes within cells. Thus, the advent of high-brilliance synchrotron and X-ray free-electron laser (XFEL) sources and the establishment of serial crystallography (SFX) have opened new avenues in structural analysis using crystals that were formerly unusable. The successful structure elucidation of cathepsin B, accomplished by the use of microcrystals obtained by in vivo crystallization in baculovirus-infected Sf9 insect cells, clearly proved that crystals grown intracellularly are very well suited for X-ray analysis. Here, methods by which in vivo crystals can be obtained, isolated and used for structural analysis by novel highly brilliant XFEL and synchrotron-radiation sources are summarized and discussed.

Serial crystallography on in vivo grown microcrystals using synchrotron radiation.

Crystal structure determinations of biological macromolecules are limited by the availability of sufficiently sized crystals and by the fact that crystal quality deteriorates during data collection owing to radiation damage. Exploiting a micrometre-sized X-ray beam, high-precision diffractometry and shutterless data acquisition with a pixel-array detector, a strategy for collecting data from many micrometre-sized crystals presented to an X-ray beam in a vitrified suspension is demonstrated. By combining diffraction data from 80 Trypanosoma brucei procathepsin B crystals with an average volume of 9 µm(3), a complete data set to 3.0 Šresolution has been assembled. The data allowed the refinement of a structural model that is consistent with that previously obtained using free-electron laser radiation, providing mutual validation. Further improvements of the serial synchrotron crystallography technique and its combination with serial femtosecond crystallography are discussed that may allow the determination of high-resolution structures of micrometre-sized crystals.

TRAF5 deficiency accelerates atherogenesis in mice by increasing inflammatory cell recruitment and foam cell formation.

RATIONALE: Tumor necrosis factor receptor-associated factors (TRAFs) are cytoplasmic adaptor proteins for the TNF/interleukin-1/Toll-like receptor superfamily. Ligands of this family comprise multiple important cytokines such as TNFα, CD40L, and interleukin-1ß that promote chronic inflammatory diseases such as atherosclerosis. We recently reported overexpression of TRAF5 in murine and human atheromata and that TRAF5 promotes inflammatory functions of cultured endothelial cells and macrophages. OBJECTIVE: This study tested the hypothesis that TRAF5 modulates atherogenesis in vivo. METHODS AND RESULTS: Surprisingly, TRAF5(-/-)/LDLR(-/-) mice consuming a high-cholesterol diet for 18 weeks developed significantly larger atherosclerotic lesions than did TRAF5(+/+)/LDLR(-/-) controls. Plaques of TRAF5-deficient animals contained more lipids and macrophages, whereas smooth muscle cells and collagen remained unchanged. Deficiency of TRAF5 in endothelial cells or in leukocytes enhanced adhesion of inflammatory cells to the endothelium in dynamic adhesion assays in vitro and in murine vessels imaged by intravital microscopy in vivo. TRAF5 deficiency also increased expression of adhesion molecules and chemokines and potentiated macrophage lipid uptake and foam cell formation. These findings coincided with increased activation of JNK and appeared to be independent of TRAF2. Finally, patients with stable or acute coronary heart disease had significantly lower amounts of TRAF5 mRNA in blood compared with healthy controls. CONCLUSIONS: Unexpectedly, TRAF5 deficiency accelerates atherogenesis in mice, an effect likely mediated by increased inflammatory cell recruitment to the vessel wall and enhanced foam cell formation.

Tumor necrosis factor receptor-associated factor 1 (TRAF1) deficiency attenuates atherosclerosis in mice by impairing monocyte recruitment to the vessel wall.

BACKGROUND: Members of the tumor necrosis factor superfamily, such as tumor necrosis factor-alpha, potently promote atherogenesis in mice and humans. Tumor necrosis factor receptor-associated factors (TRAFs) are cytoplasmic adaptor proteins for this group of cytokines. METHODS AND RESULTS: This study tested the hypothesis that TRAF1 modulates atherogenesis in vivo. TRAF1(-/-)/LDLR(-/-) mice that consumed a high-cholesterol diet for 18 weeks developed significantly smaller atherosclerotic lesions than LDLR(-/-) (LDL receptor-deficient) control animals. As the most prominent change in histological composition, plaques of TRAF1-deficient animals contained significantly fewer macrophages. Bone marrow transplantations revealed that TRAF1 deficiency in both hematopoietic and vascular resident cells contributed to the reduction in atherogenesis observed. Mechanistic studies showed that deficiency of TRAF1 in endothelial cells and monocytes reduced adhesion of inflammatory cells to the endothelium in static and dynamic assays. Impaired adhesion coincided with reduced cell spreading, actin polymerization, and CD29 expression in macrophages, as well as decreased expression of the adhesion molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in endothelial cells. Small interfering RNA studies in human cells verified these findings. Furthermore, TRAF1 messenger RNA levels were significantly elevated in the blood of patients with acute coronary syndrome. CONCLUSIONS: TRAF1 deficiency attenuates atherogenesis in mice, most likely owing to impaired monocyte recruitment to the vessel wall. These data identify TRAF1 as a potential treatment target for atherosclerosis.

Efficient production of extracellular proteins with Escherichia coli by means of optimized coexpression of bacteriocin release proteins.

Aiming to facilitate the accessibility of recombinant proteins produced with Escherichia coli, extracellular expression may be achieved by means of bacteriocin release protein (BRP) coexpression. Different types of BRPs were tested in order to optimize protein secretion into the culture medium. Those included the well-studied BRPs of the Colicin E1 and Cloacin DF13 bacteriocins and variants thereof. BRP expression was stringently controlled by means of the arabinose inducible P(BAD) promoter, which accounts for a broad-range adjustment of expression strength. Using appropriate arabinose concentrations, a concentration range was determined, that allowed efficient secretion of the model proteins alkaline phosphatase and beta-lactamase, with 90-95% of the proteins released into the culture medium. Kinetic investigations into BRP expression and protein secretion revealed a rapid increase of extracellular protein concentration within 5-10 min past induction. Alternatively to fine-tuned BRP expression during cultivation, protein production and secretion could be decoupled by establishment of appropriate induction strategies and up to 90% of alkaline phosphatase was released into the culture medium within 3h after reaching maximum biomasss concentrations. Both, fine-tuned and growth decoupled BRP expression accounted for extracellular alkaline phosphatase concentrations of roughly 500 mg l(-1) of culture broth and selectivities of 50mg of this enzyme per gram of cell dry mass, respectively.

Extracellular production and affinity purification of recombinant proteins with Escherichia coli using the versatility of the maltose binding protein.

Recombinant proteins are essential products of today's industrial biotechnology. In this study we address two crucial factors in recombinant protein production: (i) product accessibility and (ii) product recovery. Escherichia coli, one of the most frequently used hosts for recombinant protein expression, does not inherently secrete proteins into the extracellular environment. The major drawback of this expression system is, therefore, to be found in the intracellular protein accumulation and hampered product accessibility. We have constructed a set of expression vectors in order to facilitate extracellular protein production and purification. The maltose binding protein from E. coli is used as fusion partner for several proteins of interest allowing an export to the bacteria's periplasm via both the Sec and the Tat pathway. Upon coexpression of a modified Cloacin DF13 bacteriocin release protein, the hybrid proteins are released into the culture medium. This essentially applies to a distinguished reporter molecule, the green fluorescent protein, for which an extracellular production was not reported so far. The sequestered proteins can be purified to approximate homogeneity by a simple, rapid and cheap procedure which utilizes the affinity of the maltose binding protein to alpha-1,4-glucans.