Biochemical characterization of specific Alanine Decarboxylase (AlaDC) and its ancestral enzyme Serine Decarboxylase (SDC) in tea plants (Camellia sinensis)

BackgroundAlanine decarboxylase (AlaDC), specifically present in tea plants, is crucial for theanine biosynthesis. Serine decarboxylase (SDC), found in many plants, is a protein most closely related to AlaDC. To investigate whether the new gene AlaDC originate from gene SDC and to determine the biochemical properties of the two proteins from Camellia sinensis, the sequences of CsAlaDC and CsSDC were analyzed and the two proteins were over-expressed, purified, and characterized.ResultsThe results showed that exon-intron structures of AlaDC and SDC were quite similar and the protein sequences, encoded by the two genes, shared a high similarity of 85.1%, revealing that new gene AlaDC originated from SDC by gene duplication. CsAlaDC and CsSDC catalyzed the decarboxylation of alanine and serine, respectively. CsAlaDC and CsSDC exhibited the optimal activities at 45 degrees C (pH8.0) and 40 degrees C (pH7.0), respectively. CsAlaDC was stable under 30 degrees C (pH7.0) and CsSDC was stable under 40 degrees C (pH6.0-8.0). The activities of the two enzymes were greatly enhanced by the presence of pyridoxal-5-phosphate. The specific activity of CsSDC (30,488IU/mg) was 8.8-fold higher than that of CsAlaDC (3467IU/mg).Conclusions Comparing to CsAlaDC, its ancestral enzyme CsSDC exhibited a higher specific activity and a better thermal and pH stability, indicating that CsSDC acquired the optimized function after a longer evolutionary period. The biochemical properties of CsAlaDC might offer reference for theanine industrial production.

Automated summary

In this study, it was found that the new gene AlaDC originated from the gene duplication of SDC in tea plants. CsAlaDC and CsSDC exhibited optimal activities and stability at different temperatures and pH levels. CsSDC showed a much higher specific activity than CsAlaDC. These findings provide insights into the evolution and biochemical properties of AlaDC and SDC in tea plants.