Directed Evolution of Mycobacterium tuberculosis beta-Lactamase Reveals Gatekeeper Residue That Regulates Antibiotic Resistance and Catalytic Efficiency

作者：Feiler Christian; Fisher Adam C; Boock Jason T; Marrichi Matthew J; Wright Lori; Schmidpeter Philipp A M; Blankenfeldt Wulf; Pavelka Martin; DeLisa Matthew P^*

来源：PLos One, 2013, 8(9): e73123.

DOI：10.1371/journal.pone.0073123

Directed evolution can be a powerful tool for revealing the mutational pathways that lead to more resistant bacterial strains. In this study, we focused on the bacterium Mycobacterium tuberculosis, which is resistant to members of the beta-lactam class of antibiotics and thus continues to pose a major public health threat. Resistance of this organism is the result of a chromosomally encoded, extended spectrum class A beta-lactamase, BlaC, that is constitutively produced. Here, combinatorial enzyme libraries were selected on ampicillin to identify mutations that increased resistance of bacteria to beta-lactams. After just a single round of mutagenesis and selection, BlaC mutants were evolved that conferred 5-fold greater antibiotic resistance to cells and enhanced the catalytic efficiency of BlaC by 3-fold compared to the wild-type enzyme. All isolated mutants carried a mutation at position 105 (e.g., broken vertical bar 105F) that appears to widen access to the active site by 3.6 angstrom while also stabilizing the reorganized topology. In light of these findings, we propose that broken vertical bar 105 is a %26apos;gatekeeper%26apos; residue of the active site that regulates substrate hydrolysis by BlaC. Moreover, our results suggest that directed evolution can provide insight into the development of highly drug resistant microorganisms.

• 出版日期2013-9-4