| Summary: | MomL is a marine-derived quorum-quenching (QQ) lactonase which can degrade various <i>N</i>-acyl homoserine lactones (AHLs). Intentional modification of MomL may lead to a highly efficient QQ enzyme with broad application potential. In this study, we used a rapid and efficient method combining error-prone polymerase chain reaction (epPCR), high-throughput screening and site-directed mutagenesis to identify highly active MomL mutants. In this way, we obtained two candidate mutants, MomL<sub>I144V</sub> and MomL<sub>V149A</sub>. These two mutants exhibited enhanced activities and blocked the production of pathogenic factors of <i>Pectobacterium carotovorum</i> subsp. <i>carotovorum (Pcc)</i>. Besides, seven amino acids which are vital for MomL enzyme activity were identified. Substitutions of these amino acids (E238G/K205E/L254R) in MomL led to almost complete loss of its QQ activity. We then tested the effect of MomL and its mutants on <i>Pcc</i>-infected Chinese cabbage. The results indicated that MomL and its mutants (MomL<sub>L254R</sub>, MomL<sub>I144V</sub>, MomL<sub>V149A</sub>) significantly decreased the pathogenicity of <i>Pcc</i>. This study provides an efficient method for QQ enzyme modification and gives us new clues for further investigation on the catalytic mechanism of QQ lactonase.
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