Molecular insights and functional analysis of isocitrate dehydrogenase in two gram-negative pathogenic bacteria

Klebsiella pneumoniae and Legionella pneumophila are common Gram-negative bacteria that can cause lung infections. The multidrug resistance of K. pneumoniae presents a significant challenge for treatment. This study focuses on isocitrate dehydrogenase (IDH), a key enzyme in the oxidative metabolic pathway of these two bacteria. KpIDH and LpIDH were successfully overexpressed and purified, and their biochemical characteristics were thoroughly investigated. The study revealed that KpIDH and LpIDH are homodimeric enzymes with molecular weights of approximately 70 kDa. They are completely dependent on the coenzyme NADP⁺ and are inactive towards NAD⁺. KpIDH exhibits the highest catalytic activity at pH 8.0 in the presence of Mn²⁺ and at pH 7.8 in the presence of Mg²⁺. Its optimal catalytic performance is achieved with both ions at 55 °C. LpIDH exhibited its highest activity at pH 7.8 in the presence of Mn²⁺ and Mg²⁺, respectively, and exhibits optimal catalytic performance at 45 °C. Heat inactivation studies showed that KpIDH and LpIDH retained over 80% of their activity after being exposed to 45 °C for 20 min. Furthermore, we successfully altered the coenzyme specificity of KpIDH and LpIDH from NADP⁺ to NAD⁺ by replacing four key amino acid residues. This study provides a comprehensive biochemical characterization of two multidrug-resistant bacterial IDHs commonly found in hospital environments. It enhances our understanding of the characteristics of pathogenic bacteria and serves as a reference for developing new therapeutic strategies.