Preliminary Crystallographic Studies On Alanine Decarboxylase(AlaDC) And Serine Decarboxylase(AtSDC) In Arabidopsis Thaliana

Camellia sinensis is a shrub or small tree belonging to the Camellia genus.The tender leaves can be used to make tea,which is a traditional Chinese drink.With the continuous exploration of the health benefits of tea and the influence of its unique taste,tea has become the most widely popular non-alcoholic drink in the world.Among tea,one of the important reasons for the health benefits and unique taste of tea is a special amino acid--theanine（γ-glutamine）,which accounts for more than 50%of all the amino acids in tea plants.Atpresent,it has been showed that theanine is synthesized from ethylamine and glutamic acid.The source of glutamic acid in tea is rich,so the accumulation of theanine is mainly influenced by ethylamine.Alanine decarboxylase catalyzes the decarboxylation of free alanine to produces ethylamine.Therefore,the accumulation of theanine in tea plant is mainly affected by alanine decarboxylase.Arabidopsis thaliana is a model organism,which is the best plant material for genetics and molecular biology research.There are about 125 million base pairs in the Arabidopsis genome,including one gene related to serine decarboxylase,which regulates the decarboxylation of serine in plants to produce ethanolamine.The serine decarboxylase can regulate the synthesis of some phospholipids in the body,which participate in the body’s metabolic cycle.In order to study the Ala DC and AtSDC biological function and protein structure domain.The amino acid sequences of these two proteins were obtained from the NCBI website and expressed in E.coli,and through different purification and crystallization experiments for the protein crystal.Alanine decarboxylase has a total of 478 amino acids.Its theoretical molecular weight is estimated to be 52.6k D.Due to the poor solubility of the protein expressed in its full length,a series of sequences are truncated and improved,and finally protein crystals with different length amino acid sequences are obtained.The crystal space group of alanine decarboxylase protein was P4₂2₁2,and the cell parameters a=142.79?,b=142.79?,c=380.86?.Serine decarboxylase has a total of 482 amino acids.Its theoretical molecular weight is estimated to be 53.0k D.It has a high homologous similarity to alanine decarboxylase.The crystal space group of serine decarboxylase protein was P2₁,and the cell parameters a=87.74?,b=97.34?,c=118.27?,α=90°,β=107.55°,γ=90°.The protein is presented as a tetramer in solution,and the crystal structure is formed by the accumulation of two dimers.One of the main chains of the protein contains 10β-Sheets and 10α-Helix.From the structure analysis,we find that the substrate binding sites of the enzyme may be Y109,P110 and Y111,and these three amino acid residues determined the catalytic substrate of the protein as serine.