链球菌神经氨酸酶的作用机制及酶活性的测定技术

神经氨酸酶不仅存在于流感病毒,在细菌中也有分布。细菌的神经氨酸酶可裂解宿主体内糖结合物末端的神经氨酸残基,有助于细菌实现在宿主体内的定殖、穿透和扩散,是细菌重要的毒力因子之一。链球菌是自然界广泛存在的人畜共患的病原菌,在多种链球菌中均可检测出神经氨酸酶。肺炎链球菌的神经氨酸酶研究最为透彻,该菌可产生3种神经氨酸酶(NanA,NanB,NanC),NanA不但可以发挥酶的催化作用,分解唾液酸残基,暴露细菌的黏附受体,还能不依赖酶活基团,辅助细菌感染宿主细胞;NanB催化后产物可作为细菌的碳源;NanC可辅助细菌入侵脑部。在无乳链球菌和猪链球菌中,神经氨酸酶的活性一直未得到确切的验证,可能是由于它们的荚膜均含有神经氨酸,所以其神经氨酸酶的活性逐渐在进化中丧失。另外一些链球菌,例如化脓链球菌和C、G、L群链球菌,其神经氨酸酶的底物偏好相近,均对唾液类黏蛋白的催化活性较强,利于链球菌在含唾液类黏蛋白的组织中扩散。在口腔链球菌和血链球菌中,神经氨酸酶破坏血液成分中的神经氨酸链。由此可见,神经氨酸酶的特异性催化作用与链球菌在宿主体内的定植部位密切相关。此外,随着科技的发展,对神经氨酸酶的活性检测,也由早期的硫代巴比妥法,转为现在的荧光值和吸光度的测定,更为便捷和敏感。本文旨在对链球菌的神经氨酸酶的作用机制、与毒力关系及酶活测定方法等研究进展作一综述,为从事相关研究的科学工作者提供参考。

Research Progress in production and measurement of neuraminidase from Streptococci spp.

Neuraminidase hydrolyzes the terminal neuraminic acid residue of glycoconjugations. It is used in bacteria for adhesion to host cells, plasma proteins, hemocyte and important barriers and for further colonization, penetration and spread. Thus, the enzyme is an important virulence factor for various bacteria. Streptococci are widely spread pathogens for zoonoses. The activity of neuraminidase could be detected in many Streptococci spp. Streptococcus pneumonia produces 3 neuraminidases (NanA, NanB, NanC). NanA not only catalyzes the sialic residue covering the adhesion receptor, but also accelerates the bacterial infection on host cells. NanB provides carbon source for the bacteria. NanC helps S. pneumonia invading into the brain. As for group B streptococcus and S. suis, the activity of neuraminidase has not been certified yet. Researchers tend to hold the view that the neuraminidase activity has lost through evolution as both kinds of bacteria contain sialic acid in their capsules. The preference for neuraminidase of S. pyogenes and group C, G and L streptococcus is similar with strong catalytic activity for saliva mucin which avails the proliferation in organizations containing saliva mucin. The neuraminidase in S. oralis and S. sanguis destroys the sialic chain in component of blood. In all, the functions of neuraminidase are closely related to the location of bacterial colonization. In the test of enzyme activity, thiobarbital is used in the 1960s. Now the fluorogenic substrate and spectrophotometric method, the more convenient and sensitive methods, are the main ways measuring the neuraminidase activity. This paper summarizes the category, properties, mechanism of neuraminidase produced by Streptococci as well as the relationship between the enzyme and virulence. The assays for detection of neuraminidase activity are also reviewed.