Overcoming cellular secretion bottlenecks: advanced secretion engineering and molecular tailoring for next-generation microbial α-amylases with enhanced industrial performance.

α-amylases are indispensable industrial biocatalysts, yet their recombinant production faces significant biochemical and cellular bottlenecks. Recent scientific advancement shifts the paradigm from traditional cloning toward a design-parameter framework, where host selection predominantly Bacillus subtilis, Pichia pastoris, and Aspergillus niger is dictated by secretion capacity, folding landscapes, and metabolic compatibility. While Escherichia coli remains a common host, its lack of efficient extracellular secretion often leads to inclusion body formation and metabolic stress. Advanced strategies are being employed to overcome these limits, including signal peptide optimization, chaperone co-expression, and the fusion of carbohydrate-binding modules (CBMs) to enhance raw-starch degradation. Furthermore, how rational design, aided by artificial intelligence and molecular dynamics simulations, enables the engineering of hyper-thermostable and alkaline-tolerant variants capable of withstanding extreme industrial processing conditions. The advent of CRISPR-Cas technology has further revolutionized the field, allowing for precise genome editing and metabolic rewiring to achieve record-breaking enzyme titers, such as 102,893 U/mL in engineered B. subtilis. By balancing transcriptional levels with enhanced secretion pathways and stress-mitigation systems, modern synthetic biology provides the tools to tailor α-amylases for specific needs, ranging from biofuel production to high-purity malto-oligosaccharide synthesis. Therefore, this comprehensive analysis underscores that reconciling host biology with enzyme biochemistry is essential for meeting global industrial demands.