SipA is required for pilus formation in Streptococcus pyogenes serotype M3.
SipA is required for pilus formation in Streptococcus pyogenes serotype M3.
复制标题
SipA 是 M3 血清型化脓性链球菌菌毛形成所必需的。
DOI：
10.1128/jb.01520-07
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发表时间：
2008
影响因子：
3.2
通讯作者：
Scott,JuneR
中科院分区：
文献类型：
--
作者：
Zahner,Dorothea;Scott,JuneR
菌毛是人类病原体化脓性链球菌（A 组链球菌 [GAS]）的主要表面特征。 T3 菌毛由 T3 蛋白（以前的 Orf100 或 Fct3）与辅助蛋白 Cpa 共价连接的聚合物组成。已在 GAS 的几个菌毛基因簇中鉴定出一种假定的信号肽酶 SipA（也称为 LepA）。我们证明 GAS 血清型 M3 菌株的 SipA2 等位基因是 T3 菌毛合成所必需的。大肠杆菌中的异源表达表明，SipA2 以及菌毛骨架蛋白 T3 和分选酶 SrtC2 是 T3 蛋白聚合所必需的。此外，我们发现SipA2也是辅助菌毛蛋白Cpa与聚合T3连接所必需的。尽管 I 型信号肽酶家族蛋白的基序部分保守，但 SipA 缺乏这些酶的高度保守且催化重要的丝氨酸和赖氨酸残基。用丙氨酸取代最接近活性位点丝氨酸的预期位置的两个丝氨酸残基中的任一个表明这些丝氨酸残基对于T3聚合来说都是可有可无的。因此，SipA 似乎不太可能充当信号肽酶。然而，在信号肽切割位点（丙氨酸到精氨酸）的 P-1 位置突变的 T3 蛋白在 SipA2 存在的情况下不稳定，表明 SipA 和 T3 之间存在相互作用。讨论了 SipA2 在 T3 菌毛形成中可能的类似伴侣的功能。
Pili are a major surface feature of the human pathogenStreptococcus pyogenes(group A streptococcus [GAS]). The T3 pilus is composed of a covalently linked polymer of protein T3 (formerly Orf100 or Fct3) with an ancillary protein, Cpa, attached. A putative signal peptidase, SipA (also called LepA), has been identified in several pilus gene clusters of GAS. We demonstrate that the SipA2 allele of a GAS serotype M3 strain is required for synthesis of T3 pili. Heterologous expression inEscherichia colishowed that SipA2, along with the pilus backbone protein T3 and the sortase SrtC2, is required for polymerization of the T3 protein. In addition, we found that SipA2 is also required for linkage of the ancillary pilin protein Cpa to polymerized T3. Despite partial conservation of motifs of the type I signal peptidase family proteins, SipA lacks the highly conserved and catalytically important serine and lysine residues of these enzymes. Substitution of alanine for either of the two serine residues closest to the expected location of an active site serine demonstrated that these serine residues are both dispensable for T3 polymerization. Therefore, it seems unlikely that SipA functions as a signal peptidase. However, a T3 protein mutated at the P-1 position of the signal peptide cleavage site (alanine to arginine) was unstable in the presence of SipA2, suggesting that there is an interaction between SipA and T3. A possible chaperone-like function of SipA2 in T3 pilus formation is discussed.