Targeted in vitro immobilization of an intact scaffoldin-borne enzymatic
pathway to induce substrate channeling
Abstract
An immobilized, cell-free system to produce isobutanol, a
next-generation biofuel, was engineered to improve its production using
biochemical approaches. A previously described approach involving random
immobilization on suspended beads was superseded by a targeted, ordered
cellulosome-based immobilization system that facilitated substrate
channeling and minimized diffusion limitations. For this purpose,
keto-acid decarboxylase, alcohol dehydrogenase, and formate
dehydrogenase were genetically fused to a specific dockerin module,
originating from different microbial species, each of which bound
selectively to a complementary cohesin-bearing scaffoldin protein.
Engineering of the fusions, as well as tuning the expression, was key to
obtaining a working efficient multi-enzyme system. This system produced
isobutanol at a titer of 5.92 g/L and 78.4% yield, which represented a
marked improvement over previous results that used a cell-free method to
produce this biofuel. This approach is promising, both as a starting
point for further expansion of biofuel production and as a general
enzyme-immobilized platform for producing biochemicals in vitro.