Novel biocatalytic modules for the cell-free conversion of cellodextrins to glucaric acid
September 24-28, 2017
Cell-free biocatalysis offers a versatile platform for the biomanufacturing of bulk or specialty chemicals due to the flexibility in assembling enzymes from different organisms in synthetic reaction pathways. Current challenges of this approach include costly enzyme preparation, low enzyme stability and efficient enzyme recycling. To overcome these challenges, we present a molecular toolbox that facilitates the simple construction of enzymes as low-cost and recyclable biocatalytic modules. The toolbox is composed of three interchangeable components: (i) inorganic matrices; (ii) matrix-specific solid-binding peptides (SBPs); and (iii) thermostable enzymes. SBPs are short amino acid sequences that can be fused genetically to proteins and direct the orientated immobilization of the resulting protein fusion onto solid matrices (1, 2). The biocatalytic module design relies on the affinity of the SBP for inorganic matrices. Single enzyme biocatalytic modules can be prepared easily consisting of one type of enzyme immobilized per matrix while a multiple enzyme biocatalytic module consists of multiple enzymes immobilized simultaneously onto the matrix. The modules can be combined rationally to generate product-specific reaction pathways and their subsequent removal from the reaction medium allows for a ‘pick, mix, and reuse’ approach, which can be optimized easily for low-cost cell-free biomanufacturing.
Recently, we have shown that it is possible to assemble single and multiple enzyme biocatalytic modules using thermostable polysaccharide-degrading enzymes and that the enzymes retain their specific hydrolytic activities upon several rounds of recycling at high temperatures (2). Here, we applied the biocatalytic modules concept for the cell-free conversion of cellodextrins to glucaric acid, via a more complex seven enzyme synthetic pathway. Glucaric acid is one of the 12 top candidates for bio-based building blocks and is a precursor for polymers, including nylons and hyperbranched polyesters (3). Its bioproduction from cellodextrins, which can be derived from organic waste, provides a sustainable alternative to the fossil-derived production of polymers. Initially, single enzyme biocatalytic modules were prepared with a silica-specific SBP fused to two enzymes of the synthetic pathway allowing for their selective immobilization onto an inexpensive silica-based matrix. The SBP mediated the binding of each enzyme onto the matrix with over 85% immobilization efficiency. When comparing the enzyme activities of the biocatalytic modules against the free enzymes, 85 and 93% of their initial activities were retained upon immobilization, respectively. Furthermore, co-immobilization of these two enzymes as a multiple enzyme module resulted in similar immobilization yields. Performance of both enzymes in the multiple enzyme module in a successive reaction revealed that they retained 70% of their activity when compared to the free enzymes. Currently, the silica-specific SBP has been incorporated into other 5 enzymes of the pathway and we are proceeding with the construction of the single and multiple enzyme biocatalytic modules and pathway assembly.
(1) Care A, Bergquist PL, Sunna A (2015) Trends in Biotechnology, 33: 259-268.
(2) Care A, Petroll K, Gibson ESY, Bergquist PL, Sunna A (2017) Biotechnology for Biofuels 10:29.
(3) Werpy T and G Petersen (2004). Results of Screening for Potential Candidates from Sugars and Synthesis Gas. National Renewable Energy Lab.
Kerstin Petroll, Peter L. Bergquist, Anwar Sunna, and Andrew Care, "Novel biocatalytic modules for the cell-free conversion of cellodextrins to glucaric acid" in "Enzyme Engineering XXIV", Pierre Monsan, Toulouse White Biotechnology, France Magali Remaud-Simeon, LISBP-INSA, University of Toulouse, France Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/enzyme_xxiv/89