Verkehrsknotenpunkt in Miniature

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Science  11 Sep 2009:
Vol. 325, Issue 5946, pp. 1320
DOI: 10.1126/science.325_1320a

Engineering microbes so that they produce desired molecules, such as the isoprenoid precursor mevalonic acid, can have the unhealthy side effect of rerouting the host's metabolism into a suboptimal configuration. Heterologous enzymes, if expressed at high levels, may rob the cell of essential metabolites or, conversely, may introduce toxic intermediates. One conceptual way around this problem would be to centralize the synthetic machinery, reducing the transit times of intermediates as they travel from one enzyme to the next, increasing local substrate concentrations, and decreasing exposure to the elements.

In this vein, Dueber et al. have developed a modular system for constructing intracellular chemical factories. They fabricated joints by adding one of three well-characterized protein-protein interaction motifs—a GTPase binding domain, a Src homology domain, or a PDZ domain—to the N terminus of the downstream biosynthetic enzyme and the corresponding peptide ligand to the C terminus of the upstream enzyme. Varying the number of peptide ligands added and, independently, the number of peptide-binding domains attached generated a range of enhanced titers over that observed when uncatenated enzymes were used; one such combination yielded 5 mM mevalonate, an increase of almost two orders of magnitude. The advantage of building a self-contained enzyme complex, akin to the fatty acid synthases, is that the orthogonal production of chemicals imposes a tolerable cost on the host organism.

Nat. Biotechnol. 27, 753 (2009).

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