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

Biochem Biophys Res Commun

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

Published: June 2011

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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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3114173PMC
http://dx.doi.org/10.1016/j.bbrc.2011.05.038DOI Listing

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