Rational Engineering of Secondary Metabolic Pathways in a Heterologous Host to Enable the Biosynthesis of Hibarimicin Derivatives with Enhanced Anti-Melanomic Activity

A 61-kb biosynthetic gene cluster(BGC),which is accountable for the biosynthesis of hibarimicin(HBM)B from Microbispora rosea subsp.hibaria TP-A0121,was heterologously expressed in Streptomyces coelicolor M1154,which generated a trace of the target products but accumulated a large amount of shunt products.Based on rational analysis of the relevant secondary metabolism,directed engineering of the biosynthetic pathways resulted in the high production of HBM B,as well as new HBM derivates with improved antitumor activity.These results not only establish a biosynthetic system to effectively synthesize HBMs-a class of the largest and most complex Type-Ⅱpolyketides,with a unique pseudo-dimeric structure-but also set the stage for further engineering and deep investigation of this complex biosynthetic pathway toward potent anticancer drugs.

Metabolic engineering of Escherichia coli for efficient ectoine production

Ectoine is a high-value stabilizer and protective agent with various applications in enzyme industry,cosmetics,and biomedi-cine.In this study,rational engineering strategies have been implemented in Escherichia coli to efficiently produce ectoine.First,the synthetic pathway of ectoine was constructed in E.coli MG1655 by introducing an artificial thermal switch system harboring the ectABC cluster from Halomonas elongate,and the resulting strain produced 1.95 g/L ectoine.Second,crr encoding the glucose-specific enzyme II domain A of phosphotransferase system and iclR encoding the glyoxylate shunt transcriptional repressor were deleted in E.coli for enhancing the oxaloacetate supply,leading to the increasement of the ectoine titer to 9.09 g/L.Third,thrA encoding the bifunctional aspartokinase/homoserine dehydrogenase was removed from the genome to weaken the competitive pathway;simultaneously,an endogenous feedback-resistant lysC was overexpressed to complement the enzymatic activity deficiency of the aspartate kinase,leading to 30.36%increase of ectoine titer.Next,the expression of phosphoenolpyruvate carboxylase was modulated with varying gradient strength promoters to accelerate the biosynthesis efficiency of ectoine.Finally,aspDH encoding aspartate dehydrogenase from Pseudomonas aeruginosa PAO1 was overexpressed to further improve the biosynthesis of ectoine.The final strain MWZ003/pFT28-ectABC-EclysC^(*)-aspDH-ppc3 produced 30.37 g/L ectoine after 36-h fed-batch fermentation with a yield of 0.132 g/g glucose and a productivity of 0.844 g/(L h).

High-fructose corn syrup production and its new applications for 5-hydroxymethylfurfural and value-added furan derivatives:Promises and challenges

High fructose corn syrup has been industrially produced by converting glucose to fructose by glucose isomerases,tetrameric metalloenzymes widely used in industrial biocatalysis.Advances in enzyme engineering and commercial production of glucose isomerase have paved the way to explore more efficient variants of these enzymes.The 5-hydroxymethylfurfural can be produced from high fructose corn syrup catalytic dehydration,and it can be further converted into various furanic compounds chemically or biologically for various industrial applications as a promising platform chemical.Although the chemical conversion of 5-hydroxymethylfurfural into furanic compounds has been extensively investigated in recent years,bioconversion has shown promise for its mild conditions due to the harsh chemical reaction conditions.This review discusses pro-tein engineering potential for improving glucose isomerase production and recent advancements in bioconversion of 5-hydroxymethylfurfural into value-added furanic derivatives.It suggests bi-ological strategies for the industrial transformation of 5-hydroxymethylfurfural.