Division of Infectious Diseases, Department of Medicine, Emory University School of Medicine, 1639 Pierce Dr., Suite 2101, Atlanta, GA 30322, USA.
Biochem Biophys Res Commun. 2011 Jun 10;409(3):526-31. doi: 10.1016/j.bbrc.2011.05.038. Epub 2011 May 12.
Streptococcus pneumoniae type 2 pili are recently identified fimbrial structures extending from the bacterial surface and formed by polymers of the structural protein PitB. Intramolecular isopeptide bonds are a characteristic of the related pilus backbone protein Spy0128 of group A streptococci. Based on the identification of conserved residues in PitB, we predicted two intramolecular isopeptide bonds in PitB. Using a combination of tandem mass spectrometry and Edman sequencing, we show that these bonds were formed between Lys(63)-Asn(214) and Lys(243)-Asn(372) in PitB. Mutant proteins lacking the intramolecular isopeptide bonds retained the proteolytic stability observed with the wild type protein. However, absence of these bonds substantially decreased the melting temperature of the PitB-derivatives, indicating a stabilizing function of these bonds in PitB of the pneumococcal type 2 pilus.
肺炎链球菌 2 型菌毛是最近从细菌表面鉴定出的一种纤毛结构，由结构蛋白 PitB 的聚合物组成。A 组链球菌相关菌毛骨干蛋白 Spy0128 的特征是存在分子内异肽键。基于对 PitB 中保守残基的鉴定，我们预测了 PitB 中的两个分子内异肽键。通过串联质谱和 Edman 测序的组合使用，我们表明这些键是在 PitB 中的 Lys(63)-Asn(214)和 Lys(243)-Asn(372)之间形成的。缺乏分子内异肽键的突变蛋白保留了与野生型蛋白观察到的蛋白水解稳定性。然而，这些键的缺失大大降低了 PitB 衍生物的熔点，表明这些键在肺炎链球菌 2 型菌毛的 PitB 中具有稳定作用。
