Although bespoke, sequence-specific proteases have the potential to advance biotechnology and medicine, generation of proteases with tailor-made cleavage specificities remains a major challenge. We developed a phage-assisted protease evolution system with simultaneous positive and negative selection and applied it to three botulinum neurotoxin (BoNT) light-chain proteases. We evolved BoNT/X protease into separate variants that preferentially cleave vesicle-associated membrane protein 4 (VAMP4) and Ykt6, evolved BoNT/F protease to selectively cleave the non-native substrate VAMP7, and evolved BoNT/E protease to cleave phosphatase and tensin homolog (PTEN) but not any natural BoNT protease substrate in neurons. The evolved proteases display large changes in specificity (218- to >11,000,000-fold) and can retain their ability to form holotoxins that self-deliver into primary neurons. These findings establish a versatile platform for reprogramming proteases to selectively cleave new targets of therapeutic interest.

d(S)-Equol, a gut bacterial isoflavone derivative, has drawn great attention because of its potent use for relieving female postmenopausal symptoms and preventing prostate cancer. Previous studies have reported on the dietary isoflavone metabolism of several human gut bacteria and the involved enzymes for conversion of daidzein to (S)-equol. However, the anaerobic growth conditions required by the gut bacteria and the low productivity and yield of (S)-equol limit its efficient production using only natural gut bacteria. In this study, the low (S)-equol biosynthesis of gut microorganisms was overcome by cloning the four enzymes involved in the biosynthesis from Slackia isoflavoniconvertens into Escherichia coli BL21(DE3). The reaction conditions were optimized for (S)-equol production from the recombinant strain, and this recombinant system enabled the efficient conversion of 200 M and 1 mM daidzein to (S)-equol under aerobic conditions, achieving yields of 95% and 85%, respectively. Since the biosynthesis of trans-tetrahydrodaidzein was found to be a rate-determining step for (S)-equol production, dihydrodaidzein reductase (DHDR) was subjected to rational site-directed mutagenesis. The introduction of the DHDR P212A mutation increased the (S)-equol productivity from 59.0 mg/liter/h to 69.8 mg/liter/h in the whole-cell reaction. The P212A mutation caused an increase in the (S)-dihydrodaidzein enantioselectivity by decreasing the overall activity of DHDR, resulting in undetectable activity for (R)-dihydrodaidzein, such that a combination of the DHDR P212A mutant with dihydrodaidzein racemase enabled the production of (3S,4R)-tetrahydrodaidzein with an enantioselectivity of >99%.

BackgroundOmega hydroxy fatty acids (ω-OHFAs) are multifunctional compounds that act as the basis for the production of various industrial products with broad commercial and pharmaceutical implications. However, the terminal oxygenation of saturated or unsaturated fatty acids for the synthesis of ω-OHFAs is intricate to accomplish through chemocatalysis, due to the selectivity and controlled reactivity in C-H oxygenation reactions. Cytochrome P450, the ubiquitous enzyme is capable of catalyzing the selective terminal omega hydroxylation naturally in biological kingdom.ResultsTo gain a deep insight on the biochemical role of fungal P450s towards the production of omega hydroxy fatty acids, two cytochrome P450 monooxygenases from Fusarium oxysporum (FoCYP), FoCYP539A7 and FoCYP655C2; were identified, cloned, and heterologously expressed in Saccharomyces cerevisiae. For the efficient production of ω-OHFAs, the S. cerevisiae was engineered to disrupt the acyl-CoA oxidase enzyme and the β-oxidation pathway inactivated (ΔPox1) S. cerevisiae mutant was generated. To elucidate the significance of the interaction of redox mechanism, FoCYPs were reconstituted with the heterologous and homologous reductase systems - S. cerevisiae CPR (ScCPR) and F. oxysporum CPR (FoCPR). To further improve the yield, the effect of pH was analyzed and the homologous FoCYP-FoCPR system efficiently hydroxylated caprylic acid, capric acid and lauric acid into their respective ω-hydroxy fatty acids with 56%, 79% and 67% conversion. Furthermore, based on computational simulations, we identified the key residues (Asn106 of FoCYP539A7 and Arg235 of FoCYP655C2) responsible for the recognition of fatty acids and demonstrated the structural insights of the active site of FoCYPs.ConclusionFungal CYP monooxygenases, FoCYP539A7 and FoCYP655C2 with its homologous redox partner, FoCPR constitutes a promising catalyst due to its high regio- and stereo-selectivity in the hydroxylation of fatty acids and in the substantial production of industrially valuable ω-hydroxy fatty acids.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0228-2) contains supplementary material, which is available to authorized users.

Equols are isoflavandiols formed by reduction of soy isoflavones such as daidzein and genistein by gut microorganisms. These phytoestrogens are of interest for their various biological effects. We report biosynthesis from genistein to (-)-5-hydroxy-equol in recombinant E. coli expressing three reductases (daidzein reductase DZNR, dihidrodaidzein reductase DHDR, tetrahydrodaidzein reductase THDR) and a racemase (dihydrodaidzein racemase, DDRC) originating from the gut bacterium, Slackia isoflavoniconvertens. The biosynthesized 5-hydroxy-equol proved as an optically negative enantiomer, nonetheless it displayed an inverse circular dichroism spectrum to (S)-equol. Compartmentalized expression of DZNR and DDRC in one E. coli strain and DHDR and THDR in another increased the yield to 230 mg/L and the productivity to 38 mg/L/h. If the last reductase was missing, the intermediate spontaneously dehydrated to 5-hydroxy-dehydroequol in up to 99 mg/L yield. This novel isoflavene, previously not known to be synthesized in nature, was also detected in this biotransformation system. Although (S)-equol favors binding to human estrogen receptor (hER) β over hERα, (-)-5-hydroxy-equol showed the opposite preference. This study provides elucidation of the biosynthetic route of (-)-5-hydroxy-equol and measurement of its potent antagonistic character as a phytoestrogen for the first time.

A major problem of long-chain fatty acid (LCFA) hydroxylation using Escherichia coli is that FadD (long-chain fatty acyl-CoA synthetase), which is necessary for exogenous LCFA transport, also initiates cellular consumption of LCFA. In this study, an effective method to prevent the cellular consumption of LCFA without impairing its transport is proposed. The main idea is that a heterologous enzyme which consumes LCFA can replace FadD in LCFA transport. For the model heterologous enzyme, CYP153A from Marinobacter aquaeolei, which converts palmitic acid into ω-hydroxy palmitic acid, was expressed in E. coli. When fadD was deleted from an E. coli strain, CYP153A indeed maintained the ability to transport LCFA. A disadvantage of fadD deletion mutant is the fact that FadD deficiency downregulates the transcription of fadL (outer membrane LCFA transporter) via FadR (fatty acid metabolism regulator protein), was solved by fadL overexpression from a plasmid. In addition, the overexpression of fadL was able to offset catabolite repression on fadL, allowing glucose to be used as the primary carbon source. In conclusion, the strain with fadD deletion and fadL overexpression showed 5.5-fold increase in productivity compared to the wild-type strain, converting 2.6 g/L (10.0 mM) of palmitic acid into 2.4 g/L (8.8 mM) of ω-hydroxy palmitic acid in a shake flask. This simple genetic manipulation can be applied to any LCFA hydroxylation using E. coli.

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Tyrosinases (TYRs) catalyze two-step consecutive oxidation reactions of monophenolic compounds. Since known TYRs have optimal pH at neutral to somewhat basic pH, they have limitations to be used for production of catechol derivatives. In this study, we identified TYR from Burkholderia thailandensis (BtTYR), which exhibited high tyrosinase activity at low pH. We determined the crystal structure of BtTYR and provided the structural basis for the regulation of its activity in response to pH change. At high pH, BtTYR is inactivated due to the tight binding of its TYR and CAP domains, although it is stable in monomer form; at low pH, however, the protein is activated by the typical opening of the CAP domain, and the formation of tetramers maintains the stability of the protein. Such unique tyrosinase activity of BtTYR at acidic pH was successfully applied to highly efficient production of catechol derivatives and fabrication of an adhesive hydrogel.

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