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Biochem Biophys Res Commun. 2011 Jun 10;409(3):526-31. doi: 10.1016/j.bbrc.2011.05.038. Epub 2011 May 12.

Pilus backbone protein PitB of Streptococcus pneumoniae contains stabilizing intramolecular isopeptide bonds.

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  • 1Division of Infectious Diseases, Department of Medicine, Emory University School of Medicine, 1639 Pierce Dr., Suite 2101, Atlanta, GA 30322, USA.


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.

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