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Journal of Bacteriology, August 2007, p. 5716-5727, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00060-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Interactions between the Lipoprotein PilP and the Secretin PilQ in Neisseria meningitidis{triangledown} ,{dagger}

Seetha V. Balasingham,1,2 Richard F. Collins,3 Reza Assalkhou,1,2 Håvard Homberset,1,2 Stephan A. Frye,1,2 Jeremy P. Derrick,3 and Tone Tønjum1,2*

Centre for Molecular Biology and Neuroscience and Institute of Microbiology, University of Oslo, Oslo, Norway,1 Rikshospitalet-Radiumhospitalet Medical Centre, Oslo, Norway,2 Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom3

Received 11 January 2007/ Accepted 18 May 2007

Neisseria meningitidis can be the causative agent of meningitis or septicemia. This bacterium expresses type IV pili, which mediate a variety of functions, including autoagglutination, twitching motility, biofilm formation, adherence, and DNA uptake during transformation. The secretin PilQ supports type IV pilus extrusion and retraction, but it also requires auxiliary proteins for its assembly and localization in the outer membrane. Here we have studied the physical properties of the lipoprotein PilP and examined its interaction with PilQ. We found that PilP was an inner membrane protein required for pilus expression and transformation, since pilP mutants were nonpiliated and noncompetent. These mutant phenotypes were restored by the expression of PilP in trans. The pilP gene is located upstream of pilQ, and analysis of their transcripts indicated that pilP and pilQ were cotranscribed. Furthermore, analysis of the level of PilQ expression in pilP mutants revealed greatly reduced amounts of PilQ only in the deletion mutant, exhibiting a polar effect on pilQ transcription. In vitro experiments using recombinant fragments of PilP and PilQ showed that the N-terminal region of PilP interacted with the middle part of the PilQ polypeptide. A three-dimensional reconstruction of the PilQ-PilP interacting complex was obtained at low resolution by transmission electron microscopy, and PilP was shown to localize around the cap region of the PilQ oligomer. These findings suggest a role for PilP in pilus biogenesis. Although PilQ does not need PilP for its stabilization or membrane localization, the specific interaction between these two proteins suggests that they might have another coordinated activity in pilus extrusion/retraction or related functions.

* Corresponding author. Mailing address: Centre for Molecular Biology and Neuroscience, Institute of Microbiology, University of Oslo, Rikshospitalet-Radiumhospitalet Medical Centre, NO-0027 Oslo, Norway. Phone: 47 23074065. Fax: 47 23074061. E-mail: tone.tonjum{at}medisin.uio.no

{triangledown} Published ahead of print on 25 May 2007.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, August 2007, p. 5716-5727, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00060-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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