Cloning, expression, crystallization and preliminary X-ray studies of a superfolder GFP fusion of cyanobacterial Psb32

Comparative study of the insoluble and soluble Ulp1 protease constructs as Carrier free and dependent protein immobilizates

In this study, we analyzed and compared the properties of yeast Ulp1 protease in active inclusion bodies (IBs) as special protein immobilizate, and the soluble Ulp1 via oriented immobilization. Fusion of the N-terminal self-assembling peptide GFIL8 to the Ulp1 increased production of active IBs in Escherichia coli. Attachment of the N-terminal cellulose-binding module facilitated the constructed protein immobilized on the regenerated amorphous cellulose (RAC) with a binding capacity up to about 235 mg protein per gram of RAC. Compared with the immobilized soluble construct, the insoluble Ulp1 showed higher resistance to limited proteolysis with trypsin digestion, lower leaky amount at different storage temperatures, but more rapid decrease in cleavage activity after stored at 4°C for 8 days. The immobilized soluble Ulp1 maintained about 42% initial cleavage activity with repetitive use successively, whereas the aggregated Ulp1 lost its cleavage capacity after cleaving the protein substrate once. Crosslinking of IBs mediated by glutaraldehyde inactivated the Ulp1. Freshly prepared and used IBs showed similar resistance to protease-K digestion, and comparable binding capacity of Congo red and thioflavin T. Taken together, due to different advantages, the Ulp1 constructs as carrier-free and carrier-dependent immobilizates are used under different conditions.

Recent advances in synthetic biology of cyanobacteria

Cyanobacteria are attractive hosts that can be engineered for the photosynthetic production of fuels, fine chemicals, and proteins from CO₂. Moreover, the responsiveness of these photoautotrophs towards different environmental signals, such as light, CO₂, diurnal cycle, and metals make them potential hosts for the development of biosensors. However, engineering these hosts proves to be a challenging and lengthy process. Synthetic biology can make the process of biological engineering more predictable through the use of standardized biological parts that are well characterized and tools to assemble them. While significant progress has been made with model heterotrophic organisms, many of the parts and tools are not portable in cyanobacteria. Therefore, efforts are underway to develop and characterize parts derived from cyanobacteria. In this review, we discuss the reported parts and tools with the objective to develop cyanobacteria as cell factories or biosensors. We also discuss the issues related to characterization, tunability, portability, and the need to develop enabling technologies to engineer this "green" chassis.

Photosynthetic production of enantioselective biocatalysts

Background

Global resource depletion poses a dramatic threat to our society and creates a strong demand for alternative resources that do not compete with the production of food. Meeting this challenge requires a thorough rethinking of all steps of the value chain regarding their sustainability resource demand and the possibility to substitute current, petrol-based supply-chains with renewable resources. This regards also the production of catalysts for chemical synthesis. Phototrophic microorganisms have attracted considerable attention as a biomanufacturing platform for the sustainable production of chemicals and biofuels. They allow the direct utilization of carbon dioxide and do not compete with food production. Photosynthetic enzyme production of catalysts would be a sustainable supply of these important components of the biotechnological and chemical industries. This paper focuses on the usefulness of recombinant cyanobacteria for the photosynthetic expression of enantioselective catalysts. As a proof of concept, we used the cyanobacterium Synechocystis sp. PCC 6803 for the heterologous expression of two highly enantioselective enzymes.

Results

We investigated the expression yield and the usefulness of cyanobacterial cell extracts for conducting stereoselective reactions. The cyanobacterial enzyme expression achieved protein yields of 3% of total soluble protein (%TSP) while the expression in E. coli yielded 6-8% TSP. Cell-free extracts from a recombinant strain expressing the recombinant esterase ST0071 from the thermophilic organism Sulfolobus tokodai ST0071 and arylmalonate decarboxylase from Bordetella bronchiseptica showed excellent enantioselectivity (>99% ee) and yield (>91%) in the desymmetrisation of prochiral malonates.

Conclusions

We were able to present the proof-of-concept of photoautotrophic enzyme expression as a viable alternative to heterotrophic expression hosts. Our results show that the introduction of foreign genes is straightforward. Cell components from Synechocystis did not interfere with the stereoselective transformations, underlining the usability of photoautotrophic organisms for the production of enzymes. Given the considerable commercial value of recombinant biocatalysts, cyanobacterial enzyme expression has thus the potential to complement existing approaches to use phototrophic organisms for the production of chemicals and biofuels.