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

Authors
Journal
Biochemical and Biophysical Research Communications
0006-291X
Publisher
Elsevier
Publication Date
Volume
409
Issue
3
Identifiers
DOI: 10.1016/j.bbrc.2011.05.038
Keywords
  • Fimbrial Protein
  • Intramolecular Cross-Link
  • Proteolytic Stability
  • Thermal Stability
  • Mass Spectrometry
Disciplines
  • Biology

Abstract

Abstract 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 Lys63-Asn214 and Lys243-Asn372 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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