Håkansson A, Svensson M, Mossberg A K, Sabharwal H, Linse S, Lazou I, Lönnerdal B, Svanborg C
Department of Microbiology, Immunology and Glycobiology, Institute of Laboratory Medicine, Lund University, Sölvegatan 23, SE-223 62 Lund, Sweden.
Mol Microbiol. 2000 Feb;35(3):589-600. doi: 10.1046/j.1365-2958.2000.01728.x.
This study describes an alpha-lactalbumin folding variant from human milk with bactericidal activity against antibiotic-resistant and -susceptible strains of Streptococcus pneumoniae. The active complex precipitated with the casein fraction at pH 4.6 and was purified from casein by a combination of anion exchange and gel chromatography. Unlike other casein components, the active complex was retained on the ion-exchange matrix and eluted only with high salt. The eluted fraction showed N-terminal and mass spectrometric identity with human milk alpha-lactalbumin, but native alpha-lactalbumin had no bactericidal effect. Spectroscopic analysis demonstrated that the active form of the molecule was in a different folding state, with secondary structure identical to alpha-lactalbumin from human milk whey, but fluctuating tertiary structure. Native alpha-lactalbumin could be converted to the active bactericidal form by ion-exchange chromatography in the presence of a cofactor from human milk casein, characterized as a C18:1 fatty acid. Analysis of the antibacterial spectrum showed selectivity for streptococci; Gram-negative and other Gram-positive bacteria were resistant. The folding variant of alpha-lactalbumin is a new example of naturally occurring molecules with antimicrobial activity.
本研究描述了一种来自人乳的α-乳白蛋白折叠变体，它对肺炎链球菌的抗生素耐药菌株和敏感菌株具有杀菌活性。活性复合物在pH 4.6时与酪蛋白部分一起沉淀，并通过阴离子交换和凝胶色谱相结合的方法从酪蛋白中纯化出来。与其他酪蛋白成分不同，活性复合物保留在离子交换基质上，仅用高盐洗脱。洗脱部分显示与人乳α-乳白蛋白具有N端和质谱同一性，但天然α-乳白蛋白没有杀菌作用。光谱分析表明，该分子的活性形式处于不同的折叠状态，二级结构与人乳乳清中的α-乳白蛋白相同，但三级结构波动。在来自人乳酪蛋白的辅因子（一种C18:1脂肪酸）存在下，通过离子交换色谱法可将天然α-乳白蛋白转化为具有杀菌活性的形式。抗菌谱分析显示对链球菌具有选择性；革兰氏阴性菌和其他革兰氏阳性菌具有抗性。α-乳白蛋白的折叠变体是具有抗菌活性的天然存在分子的一个新例子。
