Pellegrini A, Thomas U, Bramaz N, Hunziker P, von Fellenberg R
Institute of Veterinary Physiology, Division of Applied Physiology, University of Zurich, CH-8057, Zurich, Switzerland.
Biochim Biophys Acta. 1999 Feb 2;1426(3):439-48. doi: 10.1016/s0304-4165(98)00165-2.
Proteolytic digestion of alpha-lactalbumin by pepsin, trypsin and chymotrypsin yielded three polypeptide fragments with bactericidal properties. Two fragments were obtained from the tryptic digestion. One was a pentapeptide with the sequence EQLTK (residues 1-5) and the other, GYGGVSLPEWVCTTF ALCSEK (residues (17-31)S-S(109-114)), was composed of two polypeptide chains held together by a disulfide bridge. Fragmentation of alpha-lactalbumin by chymotrypsin yielded CKDDQNPH ISCDKF (residues (61-68)S-S(75-80)), also a polypeptide composed of two polypeptide chains held together by a disulfide bridge. The three polypeptides were synthesized and found to exert antimicrobial activities. The polypeptides were mostly active against Gram-positive bacteria. Gram-negative bacteria were only poorly susceptible to the bactericidal action of the polypeptides. GYGGVSLPEWVCTTF ALCSEK was most, EQLTK least bactericidal. Replacement of leucine (23) with isoleucine, having a similar chemical structure but higher hydrophobicity, in the sequence GYGGVSLPEWVCTTF ALCSEK significantly reduced the bactericidal capacity of the polypeptide. Digestion of alpha-lactalbumin by pepsin yielded several polypeptide fragments without antibacterial activity. alpha-Lactalbumin in contrast to its polypeptide fragments was not bactericidal against all the bacterial strains tested. Our results suggest a possible antimicrobial function of alpha-lactalbumin after its partial digestion by endopeptidases.
胃蛋白酶、胰蛋白酶和胰凝乳蛋白酶对α-乳白蛋白进行蛋白水解消化后产生了三个具有杀菌特性的多肽片段。胰蛋白酶消化得到了两个片段。一个是序列为EQLTK（第1 - 5位残基）的五肽，另一个是GYGGVSLPEWVCTTF ALCSEK（第17 - 31位残基-S-S-第109 - 114位残基），由通过二硫桥连接在一起的两条多肽链组成。胰凝乳蛋白酶对α-乳白蛋白的切割产生了CKDDQNPH ISCDKF（第61 - 68位残基-S-S-第75 - 80位残基），也是一个由通过二硫桥连接在一起的两条多肽链组成的多肽。合成了这三种多肽并发现它们具有抗菌活性。这些多肽对革兰氏阳性菌大多具有活性。革兰氏阴性菌对这些多肽的杀菌作用仅表现出较弱的敏感性。GYGGVSLPEWVCTTF ALCSEK的杀菌能力最强，EQLTK最弱。在序列GYGGVSLPEWVCTTF ALCSEK中，用化学结构相似但疏水性更高的异亮氨酸取代亮氨酸（第23位），显著降低了该多肽的杀菌能力。胃蛋白酶对α-乳白蛋白的消化产生了几个没有抗菌活性的多肽片段。与它的多肽片段相比，α-乳白蛋白对所有测试的细菌菌株都没有杀菌作用。我们的结果表明，α-乳白蛋白在被内肽酶部分消化后可能具有抗菌功能。
