Regulation of NaCl on Bi-functionality of a chimeric enzyme for aromatic amino acid biosynthesis in Prevotella and Porphyromonas bacteria

Abstract

3-Deoxy-D-arabino heptulosonate-7-phosphate synthase (DAH7PS) and chorismate mutase (CM) are key enzymes in the shikimate pathway responsible for aromatic amino acid biosynthesis in bacteria. This study investigated the functional interplay between the DAH7PS and CM domains within the bifunctional enzyme PniDAH7PS-CM from Prevotella nigrescens, a representative of the chimeric enzyme group DAH7PS-CM that is primarily distributed in the Prevotella and Porphyromonas genera. Analysis of the surface polarity demonstrated that DAH7PS and CM domains rely on hetero-domain polar interactions for their catalytic functions, rather than hydrophobic contacts. We evaluated the effects of NaCl on the catalytic activity, conformation, thermal stability, and molecular aggregation of PniDAH7PS-CM at varying NaCl concentrations (0, 150, and 300 mM). Results demonstrated that increasing NaCl concentrations significantly reduced the enzymatic activities of both DAH7PS and CM, with a complete loss of DAH7PS function at 300 mM NaCl. Notably, high NaCl concentrations promoted a more extended conformation of PniDAH7PS-CM and interfere with enzyme aggregation, suggesting that NaCl modulates the inter-domain interactions. Our findings suggest that Na⁺ ions, as kosmotropic agents, likely via enhancing the hydration layer on the enzyme's surface, stabilizes PniDAH7PS-CM structure but disrupting essential polar interactions for catalysis. Conversely, Cl⁻ ions may act as chaotropic agents, further impairing these interactions. This study illuminates the balance between salt ion concentration and enzyme functionality, offering insights for developing therapeutic strategies targeting bacterial metabolism and growth in the context of periodontal diseases.