title: Pilus backbone protein PitB of Streptococcus pneumoniae contains stabilizing intramolecular isopeptide bonds.
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 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.
authors: Division of Infectious Diseases, Department of Medicine, Emory University School of Medicine, 1639 Pierce Dr., Suite 2101, Atlanta, GA 30322, USA. dzahner@emory.edu
authors: Dorothea
authors: D
authors: Zähner
authors: Ashish R
authors: AR
authors: Gandhi
authors: Olga
authors: O
authors: Stuchlik
authors: Matthew
authors: M
authors: Reed
authors: Jan
authors: J
authors: Pohl
authors: David S
authors: DS
authors: Stephens
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