The use of halogen bond is widespread in drug discovery, design, and clinical trials, but is overlooked in drug biosynthesis. Here, the role of halogen bond in the nitrilase-catalyzed synthesis of ortho-, meta-, and para-chlorophenylacetic acid was investigated. Different distributions of halogen bond induced changes of substrate binding conformation and affected substrate selectivity. By engineering the halogen interaction, the substrate selectivity of the enzyme changed, with the implication that halogen bond plays an important role in biosynthesis and should be used as an efficient and reliable tool in enzymatic drug synthesis.

Fungi of the genus Trichoderma are a rich source of enzymes, such as cellulases and hemicellulases, that can degrade lignocellulosic biomass and are therefore of interest for biotechnological approaches seeking to optimize biofuel production. The essential transcription factor ACE3 is involved in cellulase production in Trichoderma reesei; however, the mechanism by which ACE3 regulates cellulase activities is unknown. Here, we discovered that the nominal ace3 sequence in the T. reesei genome available through the Joint Genome Institute is erroneously annotated. Moreover, we identified the complete ace3 sequence, the ACE3 Zn(II)₂Cys₆ domain, and the ACE3 DNA-binding sites containing a 5′-CGGAN(T/A)₃-3′ consensus. We found that in addition to its essential role in cellulase production, ace3 is required for lactose assimilation and metabolism in T. reesei. Transcriptional profiling with RNA-Seq revealed that ace3 deletion down-regulates not only the bulk of the major cellulase, hemicellulase, and related transcription factor genes, but also reduces the expression of lactose metabolism–related genes. Additionally, we demonstrate that ACE3 binds the promoters of many cellulase genes, the cellulose response transporter gene crt1, and transcription factor–encoding genes, including xyr1. We also observed that XYR1 dimerizes to facilitate cellulase production and that ACE3 interacts with XYR1. Together, these findings uncover how two essential transcriptional activators mediate cellulase gene expression in T. reesei. On the basis of these observations, we propose a model of how the interactions between ACE3, Crt1, and XYR1 control cellulase expression and lactose metabolism in T. reesei.

Serrawettin W1 produced by Serratia marcescens is a surface-active exolipid resulting in a lot foam formation during the 2,3-butanediol (2,3-BD) fermentation process. In order to avoid excessive addition of antifoam agent and microbial contamination, S. marcescens mutants deficient in serrawettin W1 formation were successfully constructed through insertional inactivation of the swrW gene coding for serrawettin W1 synthase. The shake flask and batch experiments suggested that disruption of the swrW gene led to significant reduction of the foam formation and improved 2,3-BD production a little. Ultimately, fed-batch culturing of the mutant afforded a maximum 2,3-BD concentration of 152 g l⁻¹ with a productivity of 2.67 g l⁻¹ h⁻¹ and a yield of 92.6% at 57 h.