The peptidoglycan-degrading property of lysozyme is not required for bactericidal activity in vivo
The peptidoglycan-degrading property of lysozyme is not required for bactericidal activity in vivo
复制标题
DOI：
10.4049/jimmunol.177.1.519
复制
发表时间：
2006-07-01
影响因子：
4.4
通讯作者：
Akinbi, Henry T.
中科院分区：
文献类型：
--
作者：
Nash, James A.;Ballard, Tiffany Nicole S.;Akinbi, Henry T.
溶菌酶是一种丰富的阳离子抗菌蛋白，在肺部宿主防御中起重要作用。转基因小鼠空气中溶菌酶浓度的增加增强了细菌的杀灭，而溶菌酶缺乏导致细菌负荷和发病率增加。溶菌酶降解细菌细胞壁中的肽聚糖，导致快速杀死革兰氏阳性微生物;然而，这种机制不能解释溶菌酶对革兰氏阴性菌的保护作用。因此，本研究旨在检验溶菌酶的催化活性（溶菌酶活性）不是体内细菌杀灭所必需的假设。在小鼠溶菌酶M的53位（D53 S）处丝氨酸取代天冬氨酸完全消除了胞壁酶活性。溶菌酶缺陷型重组溶菌酶（LySM（D53 S））在体外对革兰氏阳性菌和革兰氏阴性菌均有杀灭作用。在野生型（LysM（+/+）/LysM（D53 S））或溶菌酶M缺失小鼠（LysM（-/-）/LysM（D53 S））的呼吸道上皮中靶向表达LysM（D53 S）导致空气空间中溶菌酶蛋白显著升高，而溶菌酶活性没有任何增加。用革兰氏阳性或革兰氏阴性细菌对转基因小鼠进行肠内攻击导致LysM（-/-）小鼠中细菌负荷的显著增加，这被LysM（D53 S）的靶向表达完全逆转。这些结果表明，溶菌酶的溶菌酶活性不是体外或体内杀死细菌所必需的。
Lysozyme is an abundant, cationic antimicrobial protein that plays an important role in pulmonary host defense. Increased concentration of lysozyme in the airspaces of transgenic mice enhanced bacterial killing whereas lysozyme deficiency resulted in increased bacterial burden and morbidity. Lysozyme degrades peptidoglycan in the bacterial cell wall leading to rapid killing of Gram-positive organisms; however, this mechanism cannot account for the protective effect of lysozyme against Gram-negative bacteria. The current study was therefore designed to test the hypothesis that the catalytic activity (muramidase activity) of lysozyme is not required for bacterial killing in vivo. Substitution of serine for aspartic acid at position 53 (D53S) in mouse lysozyme M completely ablated muramidase activity. Muramidase-deficient recombinant lysozyme (LySM(D53S)) killed both Gram-positive and Gram-negative bacteria in vitro. Targeted expression of LysM(D53S) in the respiratory epithelium of wild-type (LysM(+/+)/LysM(D53S)) or lysozyme M-null mice (LysM(-/-)/LysM(D53S)) resulted in significantly elevated lysozyme protein in the airspaces without any increase in muramidase activity. Intratracheal challenge of transgenic mice with Gram-positive or Gramnegative bacteria resulted in a significant increase in bacterial burden in LysM(-/-) mice that was completely reversed by targeted expression of LysM(D53S). These results indicate that the muramidase activity of lysozyme is not required for bacterial killing in vitro or in vivo.