This year, the Jiashu-CHINA team focused on the engineered construction of the HMB (3-hydroxy-3-methylbutyric acid) and serotonin (5-HT) biosynthetic pathways, aiming to explore the applications of synthetic biology in metabolic regulation and health intervention. We designed and submitted multiple basic and composite parts, covering de novo HMB synthesis, heterologous serotonin synthesis, and a biosafety suicide system, and validated their potential application value through functional characterization.

• BBa_25G48CDM (TPH, 1332 bp) – Tryptophan hydroxylase, catalyzing the conversion of tryptophan to 5-HTP, the key enzyme in serotonin synthesis.
• BBa_25P80OSX (TDC, 1503 bp) – Tryptophan decarboxylase, converting 5-HTP into serotonin.
• BBa_25BAALSN (YciA, 393 bp, Silver Prize) – Thioesterase, enhancing HMB production and improving metabolic flux.
• BBa_25VQVUES (AtoB, 1182 bp) – Acetyl-CoA acetyltransferase, catalyzing the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA, a key node in the MVA/HMB pathway.
• BBa_25PLCDZA (mvaS, 1167 bp) – HMG-CoA synthase, catalyzing the condensation of acetoacetyl-CoA and acetyl-CoA to generate HMG-CoA.
• BBa_2554PQS6 (aibA, 795 bp) – α-subunit of methylglutaconyl-CoA decarboxylase complex, responsible for decarboxylating 3-MG-CoA to 3-MC-CoA in the HMB pathway, a key step that transforms a tricarboxylate structure into an unsaturated acyl-CoA intermediate.
• BBa_25EFNVLR (aibB, 738 bp) – β-subunit of methylglutaconyl-CoA decarboxylase complex, performing the same decarboxylation function as aibA to convert 3-MG-CoA into 3-MC-CoA, facilitating the structural transformation toward HMB synthesis.
• BBa_25P2LT86 (liuC, 774 bp) – Hydratase, catalyzing the hydration of 3-MC-CoA by introducing a hydroxyl group at the C3 position, generating HMB-CoA, the direct precursor of HMB and a key step in establishing HMB’s characteristic functional group.
• BBa_25YQAEQ1 (tesB, 858 bp) – Thioesterase, promoting product release and enhancing metabolic yield.
• BBa_25A7QNVZ (MenI, 408 bp) – 1,4-dihydroxy-2-naphthoyl-CoA hydrolase, involved in menaquinone (vitamin K₂) biosynthesis, expanding host metabolic potential.
• BBa_K1096002 (mazF, 333 bp, Bronze Prize) – RNA endonuclease toxin used in constructing an arabinose-inducible suicide system.
• BBa_K808000 (araC-pBAD, 1210 bp) – Arabinose-inducible promoter, enabling external regulation of the suicide system.

• BBa_25Y42N8F (HMB de novo synthesis, 5455 bp, Gold Prize) – Integrates AtoB, mvaS, aibA, aibB, liuC, tesB, and YciA to construct a de novo HMB synthesis pathway starting from acetyl-CoA.
• BBa_25V63370 (Serotonin synthesis, 2909 bp) – Combines TPH and TDC to establish a serotonin biosynthetic module, forming the complete pathway from tryptophan to serotonin.
• BBa_25CC4XIU (araC-pBAD-mazF, 1689 bp) – Fusion of araC-pBAD with mazF, forming an arabinose-inducible suicide module for biosafety control.

• Established a complete de novo HMB pathway, providing a new tool for muscle protection, sports nutrition, and metabolic research.
• Submitted a serotonin synthesis module, offering a chassis for studying the gut-brain axis and mental health interventions.
• Optimized metabolic flux control elements (YciA, tesB, etc.), providing universal tools for metabolic engineering teams.
• Designed a controllable suicide system (araC-pBAD-mazF), improving the biosafety of engineered strains.

These parts not only support projects on HMB and serotonin, but can also be reused in future iGEM projects involving amino acid metabolism, health interventions, metabolic engineering, and biosafety system design.