Institute for Microbiology and Infection, School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK.
Medical School, School of Life Sciences, Queen's Medical Centre, University of Nottingham, Nottingham, NG7 2UH, UK.
Nat Commun. 2020 Sep 23;11(1):4817. doi: 10.1038/s41467-020-18139-8.
Lysozymes are among the best-characterized enzymes, acting upon the cell wall substrate peptidoglycan. Here, examining the invasive bacterial periplasmic predator Bdellovibrio bacteriovorus, we report a diversified lysozyme, DslA, which acts, unusually, upon (GlcNAc-) deacetylated peptidoglycan. B. bacteriovorus are known to deacetylate the peptidoglycan of the prey bacterium, generating an important chemical difference between prey and self walls and implying usage of a putative deacetyl-specific "exit enzyme". DslA performs this role, and ΔDslA strains exhibit a delay in leaving from prey. The structure of DslA reveals a modified lysozyme superfamily fold, with several adaptations. Biochemical assays confirm DslA specificity for deacetylated cell wall, and usage of two glutamate residues for catalysis. Exogenous DslA, added ex vivo, is able to prematurely liberate B. bacteriovorus from prey, part-way through the predatory lifecycle. We define a mechanism for specificity that invokes steric selection, and use the resultant motif to identify wider DslA homologues.
溶菌酶是研究最为透彻的酶类之一，作用于细胞壁底物肽聚糖。在这里，我们研究了侵袭性细菌周质捕食者蛭弧菌（Bdellovibrio bacteriovorus），发现了一种多样化的溶菌酶 DslA，它异常地作用于（GlcNAc-）去乙酰化的肽聚糖。众所周知，蛭弧菌会使猎物细菌的肽聚糖去乙酰化，在猎物和自身细胞壁之间产生重要的化学差异，这意味着可能存在一种特定的去乙酰化“出口酶”。DslA 就具有这种作用，而ΔDslA 菌株在离开猎物时会出现延迟。DslA 的结构揭示了一种经过修饰的溶菌酶超家族折叠，具有多种适应性。生化分析证实了 DslA 对去乙酰化细胞壁的特异性，并利用两个谷氨酸残基进行催化。体外添加外源 DslA 能够使 B. bacteriovorus 提前从猎物中释放出来，从而进入捕食生命周期的中间阶段。我们定义了一种特异性机制，涉及到空间位阻选择，并利用所得的基序来识别更广泛的 DslA 同源物。
