Area de Microbiología, Instituto Universitario de Biotecnología, Universidad de Oviedo, Oviedo, Spain.
Appl Microbiol Biotechnol. 2012 Apr;94(1):101-10. doi: 10.1007/s00253-011-3588-5. Epub 2011 Sep 28.
The lysin gene (lysA2) of the Lactobacillus casei bacteriophage A2 was cloned and expressed in Escherichia coli. LysA2 is an endopeptidase that hydrolyzes the bond between the terminal D: -alanine of the peptidoglycan tetrapeptide and the aspartic acid residue that forms the bridge with the L: -lysine of a neighboring peptidoglycan chain, characteristic of Gram-positive bacteria included into the A4 peptidoglycan subgroup. This includes most lactobacilli, Lactococcus lactis, Pediococcus acidilactici, and Pediococcus pentosaceus, the walls of all of which were substrates for the enzyme. Specific binding of LysA2 to the wall of these bacteria is mediated by its C-terminal moiety, does not need the N-terminal catalytic domain for recognition, and is stable: at least 88% of the molecules were still bound to L. casei after 3 days in phosphate buffer at 4°C. The enzyme acts as a monomer, is active at pH values between 4 and 6, and at temperatures ranging between 18°C and 50°C while being independent of divalent cation addition. The enzyme showed strong resistance to incubation at high and low pH values but became progressively inactivated at 50°C and above. LysA2 is bactericidal, the viability of L. casei cultures dropping to 1% in 10 min, under the standard conditions used for the enzymatic assay.
乳酸乳球菌噬菌体 A2 的溶菌酶基因 (lysA2) 在大肠杆菌中被克隆和表达。LysA2 是一种内肽酶，可水解肽聚糖四肽末端的 D: -丙氨酸与形成桥接的天冬氨酸残基与相邻肽聚糖链上的 L: -赖氨酸之间的键，这是包括在 A4 肽聚糖亚群中的革兰氏阳性菌的特征。这包括大多数乳杆菌、乳球菌 lactis、戊糖片球菌和乳酸片球菌，它们的细胞壁都是该酶的底物。LysA2 对这些细菌细胞壁的特异性结合是由其 C 末端介导的，不需要识别 N 端催化结构域，并且稳定：在 4°C 的磷酸盐缓冲液中至少 88%的分子在 3 天后仍与 L. casei 结合。该酶作为单体发挥作用，在 pH 值为 4 到 6 之间、温度在 18°C 到 50°C 之间时具有活性，并且不依赖于二价阳离子的添加。该酶对在高 pH 值和低 pH 值下孵育表现出很强的抗性，但在 50°C 以上时逐渐失活。LysA2 具有杀菌作用，在用于酶测定的标准条件下，L. casei 培养物的存活率在 10 分钟内下降到 1%。
