Structural and Enzymological Characterization of Phosphoserine Phosphatase From Brucella melitensis

Amino acid L-serine (L-Ser) is a precursor of various biomolecules, including other amino acids, glutathione, and nucleotides. The metabolism of this amino acid is crucial in diseases such as brucellosis. Previous studies have revealed that the enzymes involved in L-Ser biosynthesis are essential for Brucella replication, making them potential targets for the development of new drugs. Here, we focus on Brucella melitensis phosphoserine phosphatase (BmPSP), which catalyzes the dephosphorylation of phosphoserine in L-Ser. The enzyme is characterized through enzymatic and structural studies, leading to the discovery of its first crystallographic structures. The interactions of BmPSP with different ligands are also investigated. We demonstrate that the substitution of its Mg²⁺ cofactor with Ca²⁺ inhibits the enzyme and results in a slight movement of catalytic residues in the active site. Crystallographic structures of BmPSP in complex with substrate, reaction products, and substrate analogs are also detailed, revealing the interaction between these molecules and the active site residues. This structural study provides a better understanding of phosphoserine phosphatases, highlighting the involvement of two highly conserved residues in the mechanism of substrate entry into the active site.