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

► Two intramolecular isopeptide bonds are present in PitB of Streptococcus pneumoniae. ► Intramolecular isopeptide bonds are not required for proteolytic stability of PitB. ► Intramolecular isopeptide bonds confer thermal stability to PitB.