Fig. 4.

Overview of strategies for engineering of rate-limiting bio-parts in heterologous biosynthesis. I Promoter engineering is used for fine-tuning of gene expression via screening and characterization of native promoter pool as well as construction of synthetic promoter library. II Protein engineering is employed to optimize enzymatic properties via directed evolution and rational design. III Cofactor engineering is adopted to improve the supply of reducing forces by regulation of endogenous cofactor system or introduction of heterologous cofactor regeneration systems. IV Transporter mining is applied to eliminate the transportation bottlenecks via omics analysis and literature retrieval