Laboratory of Bacterial Pathogenesis and Immunology, Rockefeller University, New York, NY 10065.
Microbiol Spectr. 2019 Jul;7(4). doi: 10.1128/microbiolspec.GPP3-0012-2018.
Surface proteins are critical for the survival of gram-positive bacteria both in the environment and to establish an infection. Depending on the organism, their surface proteins are evolutionarily tailored to interact with specific ligands on their target surface, be it inanimate or animate. Most surface molecules on these organisms are covalently anchored to the peptidoglycan through an LPxTG motif found at the C-terminus. These surface molecules are generally modular with multiple binding or enzymatic domains designed for a specific survival function. For example, some molecules will bind serum proteins like fibronectin or fibrinogen in one domain and have a separate function in another domain. In addition, enzymes such as those responsible for the production of ATP may be generally found on some bacterial surfaces, but when or how they are used in the life of these bacteria is currently unknown. While surface proteins are required for pathogenicity but not viability, targeting the expression of these molecules on the bacterial surface would prevent infection but not death of the organism. Given that the number of different surface proteins could be in the range of two to three dozen, each with two or three separate functional domains (with hundreds to thousands of each protein on a given organism), exemplifies the complexity that exists on the bacterial surface. Because of their number, we could not adequately describe the characteristics of all surface proteins in this chapter. However, since the streptococcal M protein was one of the first gram-positive surface protein to be completely sequenced, and perhaps one of the best studied, we will use M protein as a model for surface proteins in general, pointing out differences with other surface molecules when necessary.
表面蛋白对于革兰氏阳性菌在环境中的生存和引发感染至关重要。根据不同的生物体，其表面蛋白经过进化，能够与目标表面上特定的配体相互作用，无论是无生命的还是有生命的。这些生物体上的大多数表面分子通过位于 C 末端的 LPxTG 模体共价锚定到肽聚糖上。这些表面分子通常是模块化的，具有多个结合或酶结构域，用于特定的生存功能。例如，一些分子在一个结构域中结合血清蛋白（如纤维连接蛋白或纤维蛋白原），而在另一个结构域中具有单独的功能。此外，负责产生 ATP 的酶等可能普遍存在于某些细菌表面，但目前尚不清楚它们在这些细菌的生命中何时或如何使用。虽然表面蛋白对于致病性是必需的，但不是生存所必需的，靶向细菌表面这些分子的表达可以防止感染，但不会导致生物体死亡。鉴于不同的表面蛋白数量可能在 20 到 30 个之间，每个蛋白都有两个或三个独立的功能结构域（给定生物体上每个蛋白的数量可能达到数百到数千个），这说明了细菌表面存在的复杂性。由于数量众多，我们无法在本章中充分描述所有表面蛋白的特征。然而，由于链球菌 M 蛋白是最早被完全测序的革兰氏阳性表面蛋白之一，也是研究得最多的蛋白之一，因此我们将使用 M 蛋白作为一般表面蛋白的模型，在必要时指出与其他表面分子的差异。
