Identification of histidine decarboxylase and its multi-enzyme cascade system for cost-efficient biosynthesis of carcinine.

Unlabelled: Carcinine, a bioactive compound with antioxidant and anti-glycation properties, holds significant promise for applications in pharmaceuticals and cosmetics. This study demonstrates a novel strategy for the direct biosynthesis of carcinine from low-cost L-histidine and β-alanine using a multi-enzyme cascade system. A highly efficient histidine decarboxylase (PphHDC) was identified. Following vector optimization and induction parameter tuning, soluble expression of PphHDC was systematically enhanced in the BPH-2 strain (BL21(DE3) harboring pACYC-) under optimal conditions: 37 °C, 0.1 mM IPTG, and 8 h induction. Further, the optimally expressed PphHDC achieved the optimal enzymatic activity of 7.76 U/mg under conditions of pH 6.0, 30 °C, and 5 mM Ca⁺. To facilitate carcinine synthesis, PphHDC was integrated with the previously reported SGE (Sfp-GSG-Ebony) enzyme in three catalytic systems: single-cell, dual-cell whole-cell catalysis, and multi-enzyme cascade. Among these, the multi-enzyme cascade system, comprising purified soluble PphHDC and SGE-D (engineered with an N-terminal DsbA tag to enhance solubility), achieved the highest efficiency. This system produced a maximum carcinine titer of 4.29 mM with a yield of 0.18 mM/h within 24 h, representing the highest reported conversion from L-histidine and β-alanine. These findings establish a robust foundation for cost-effective industrial production of carcinine. The study highlights the importance of fine-tuning heterologous expression systems to balance protein solubility and productivity in biocatalytic applications.

Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-025-04467-3.