Intramolecular amide bonds stabilize pili on the surface of bacilli
- Jonathan M. Budzika,1,
- Catherine B. Poorb,1,
- Kym F. Faullc,
- Julian P. Whiteleggec,
- Chuan Heb,1 and
- Olaf Schneewinda,1
- aDepartments of Microbiology and
- bChemistry, University of Chicago, Chicago, IL 60637; and
- cPasarow Mass Spectrometry Laboratory, Neuropsychiatric Institute, Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
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Communicated by Robert Haselkorn, University of Chicago, Chicago, IL, September 28, 2009
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↵1J.M.B. and C.B.P. contributed equally to this work. (received for review July 29, 2009)
Abstract
Gram-positive bacteria elaborate pili and do so without the participation of folding chaperones or disulfide bond catalysts. Sortases, enzymes that cut pilin precursors, form covalent bonds that link pilin subunits and assemble pili on the bacterial surface. We determined the x-ray structure of BcpA, the major pilin subunit of Bacillus cereus. The BcpA precursor encompasses 2 Ig folds (CNA2 and CNA3) and one jelly-roll domain (XNA) each of which synthesizes a single intramolecular amide bond. A fourth amide bond, derived from the Ig fold of CNA1, is formed only after pilin subunits have been incorporated into pili. We report that the domains of pilin precursors have evolved to synthesize a discrete sequence of intramolecular amide bonds, thereby conferring structural stability and protease resistance to pili.
Footnotes
- 2To whom correspondence may be addressed. E-mail: oschnee{at}bsd.uchicago.edu or chuanhe{at}uchicago.edu
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Author contributions: J.M.B., C.B.P., K.F.F., J.P.W., C.H., and O.S. designed research; J.M.B., C.B.P., K.F.F., and J.P.W. performed research; J.M.B., C.B.P., K.F.F., J.P.W., C.H., and O.S. contributed new reagents/analytic tools; J.M.B., C.B.P., K.F.F., J.P.W., C.H., and O.S. analyzed data; and J.M.B., C.B.P., C.H., and O.S. wrote the paper.
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The authors declare no conflict of interest.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0910887106/DCSupplemental.
