<b>Kinetic and homology model analysis of diaminopimelate decarboxylase from</b> <i>Cyanothece</i> <b>sp. ATCC 51142: unveiling a key enzyme in lysine biosynthesis</b>

Diaminopimelate decarboxylase (DAPDC), a pyridoxal 5'-phosphate (PLP)-dependent enzyme, catalyzes the decarboxylation of diaminopimelate (DAP) to yield L-lysine, a key step in lysine biosynthesis. This present study presents a preliminary characterization of DAPDC encoded by the cce1351 gene in Cyanothece sp. ATCC 51142 (CsDAPDC), focusing on its biochemical properties and model structure characteristics. The enzyme exhibited a peak activity at 30°C and pH 8.0, and the catalytic constant (kcat) and substrate binding affinity Michaelis constant (KM) were determined as 1.68 s-1 and 1.20 mM at the above-mentioned condition, respectively. Homology modeling and molecular docking analysis revealed that Gly286, Gly330, Tyr428, and Asp118 interacted with the PLP cofactor, and Ser249, Tyr372, and Tyr428 interacted with the DAP substrate. Additionally, Cys399, Glu400, and Tyr436 from the other monomer were also involved in binding DAP and PLP. Site-directed mutagenesis confirmed the functional roles of these key residues in catalysis. This work provides valuable insights into the catalytic mechanism of CsDAPDC and highlights the enzyme's potential for applications in metabolic engineering of cyanobacteria for enhanced lysine production.