Yet more intramolecular cross-links in Gram-positive surface proteins.
Yet more intramolecular cross-links in Gram-positive surface proteins.
复制标题
革兰氏阳性表面蛋白中存在更多分子内交联。
DOI：
10.1073/pnas.1322482111
复制
发表时间：
2014
影响因子：
11.1
通讯作者：
Schwarz-Linek U
中科院分区：
文献类型：
--
作者：
Schwarz-Linek U
革兰氏阳性细菌的表面包括单层膜，并且通常包括赋予强度和刚性的交联肽聚糖的厚层。锚定到该细胞壁的是蛋白质组装体，例如皮利，和表面蛋白质，例如作为表面粘附素的微生物表面组分识别粘附基质分子（MSCRAlectin）。这些蛋白质不仅在感染的早期阶段对细菌与宿主表面的结合至关重要，而且对生物膜形成和免疫逃避也至关重要。在2007年以来发表的一系列研究中，这些细胞表面蛋白质和蛋白质组装体已被证明含有异肽和硫酯键，氨基酸侧链之间极不寻常的分子内共价键。这些交联具有稳定结构的作用，或者可能直接参与粘附。使用结构生物学和质谱的优雅组合，Kwon et al. (1)在PNAS中揭示了酯键作为来自革兰氏阳性病原体产气荚膜梭菌的推定MSCRAMM中的另一个共价键。值得注意的是，这种酯键，连接的一个苏氨酸和谷氨酰胺残基的侧链，相当于一个未解决的酰基酶中间体，形成的自催化途径，类似于丝氨酸蛋白酶的机制。尽管它们在细菌基因组中编码的方式存在根本性差异，但在细胞表面递送/组装后，皮利和许多MSCRA具有重要的相似性。在这些蛋白质中，一系列重复结构域（通常称为茎区）负责结构的长度，并允许N-末端区域远离细胞表面定位。在C末端，皮利和MSCRAf 1通过分选酶锚定在细胞壁上（2）。尽管革兰氏阳性表面蛋白和皮利的许多结构单元与它们的革兰氏阴性等同物有一些相似之处（它们是Ig样β-夹心折叠的变体），但它们的组装机制非常不同（3）。如上所述，自从革兰氏阳性皮利的分子表征以来，一些更显著的发现是在组分蛋白中分子内共价键的普遍存在。这些键中的第一个是在人类病原体化脓性链球菌的皮利的柄蛋白中发现的（6）。这些分子内的异肽键现在已经在实验上在来自许多革兰氏阳性病原体的广泛的菌毛亚基中得到了表征（在参考文献中进行了综述）。7-9)以及MSCRAMM FbaB（10）中。分子内异肽键最常形成于Lys和Asn残基的侧链之间（图1）[尽管也存在Lys-Asp键（10，11）]。包含这些键的残基被策略性地定位以桥接第一个和倒数第二个或最后一个键。
The surface of Gram-positive bacteria comprises a single membrane and, typically, a thick layer of cross-linked peptidoglycan that imparts strength and rigidity. Anchored to this cell wall are protein assemblies, such as pili, and surface proteins, such as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) that act as surface adhesins. These proteins are critical not only for bacterial binding to host surfaces in the early stages of infection but also for biofilm formation and immune evasion. In a series of studies published since 2007, these cell surface proteins and protein assemblies have been shown to contain isopeptide and thioester bonds, highly unusual intramolecular covalent linkages between amino acid side chains. These cross-links have either a structure-stabilizing role or may be directly involved in adhesion. Using an elegant combination of structural biology and mass spectrometry, Kwon et al.(1) reveal in PNAS an ester bond as yet another covalent linkage in a putative MSCRAMM from the Grampositive pathogen Clostridium perfringens. Remarkably, this ester bond, joining the side chains of a Thr and Gln residue, is equivalent to an unresolved acyl-enzyme intermediate, formed on an autocatalytic pathway that resembles the mechanism of serine proteases. Despite fundamental differences in the way they are encoded in bacterial genomes, following delivery/assembly at the cell surface, pili and many MSCRAMMs share important similarities. In such proteins, a series of repetitive domains (commonly referred to as stalk regions) are responsible for the length of the structure and allow an N-terminal region to be positioned away from the cell surface. At the C terminus, both pili and MSCRAMMs are anchored to the cell wall by sortases (2). Although many of the building blocks of Gram-positive surface proteins and pili bear some resemblance to their Gramnegative equivalents (they are variants of the Ig-like β-sandwich fold), their mechanisms of assembly are very different (3). As mentioned above, some of the more remarkable discoveries made since the molecular characterization of Gram-positive pili (4, 5) are the prevalence of intramolecular covalent linkages in the component proteins. The first of these bonds was discovered in the stalk protein of pili from the human pathogen Streptococcus pyogenes (6). These intramolecular isopeptide bonds have now been characterized experimentally in a wide-range of pilus subunits from many Gram-positive pathogens (reviewed in refs. 7–9) and also in the MSCRAMM FbaB (10). Intramolecular isopeptide bonds are most commonly formed between the side chains of Lys and Asn residues (Fig. 1)[although Lys-Asp bonds also exist (10, 11)]. The residues comprising these bonds are strategically positioned to bridge the first and either penultimate or last