Distant Site Mutations in Clinical TEM Beta-Lactamase Variants Enhance Non-Covalent Binding to Ceftazidime: Insights from Spectroscopic and Biophysical Investigations.

β-lactamases retain the central armamentarium against the β-lactams, resulting in surge of antibiotic resistance, primarily due to the hydrolysis of the amide bond of the four-membered ring. This study aimed to investigate the binding interactions of ceftazidime (CAZ) to TEM β-lactamase variants with distant site mutations isolated from clinical setting to explore the cause of their selection and dissemination due to indiscriminate use of β-lactams. Absorbance and fluorescence spectroscopy along with biophysical experimentation indicated facilitated binding of CAZ to the active site of the mutants than the wild type. The CAZ-TEM β-lactamase mutant interactions were predominantly hydrophobic compared to H-bonding and van der Waals forces in the CAZ-wild type complex. Additionally structural alteration to justify more rigid binding of CAZ to the mutants in contrast to the wild type enzyme was established in silico. Therefore, acquisition of distant site mutations with respect to the active site of the β-lactamase variants that rendered conformational flexibility to accommodate CAZ was evidenced. This study provided an insight to the bioactive interaction of CAZ with TEM β-lactamase variants that probably facilitated their selection from clinical settings in response to rampant usage of β-lactams.