Structure and Assembly of Type IV Pilins

Katrina T. Forest

doi:10.1128/9781555818395.ch6

Chapter 6 : Structure and Assembly of Type IV Pilins

Author: Katrina T. Forest¹

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Affiliations: 1: Department of Bacteriology, University of Wisconsin—Madison, Madison, WI 53706

Content Type: Monograph

Publication Year: 2005

Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis

Book DOI: 10.1128/9781555818395

Chapter DOI: 10.1128/9781555818395.ch6

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Abstract:

This chapter focuses on the contribution of structural biology to the understanding of the type IV pili. Recent reviews cover the developments in research on molecular genetics, regulation of expression and assembly, pilus-mediated surface motility, host responses to pili, and pilus-based vaccines carried out by many laboratories around the world. High-resolution structures of four type IV pilins have been published. In the chapter, the structural details of each pilin subunit are elaborated and compared. Models for pilus filament assembly based on the monomer structures are also discussed. The limited structural information available for pilus assembly proteins is summarized. The chapter is an appropriate venue in which to clarify that type IV pilus filament models are not refined atomic resolution structures of pilus quatenary assemblies. To increase the accuracy and resolution of any type IV pilus assembly model, the model must be rigorously refined against moderate-resolution data for intact pili, such as cryoelectron microscopy reconstructions or complete high-resolution fiber diffraction data sets. These have been challenging to obtain for the very smooth and thin type IV pili. X-ray crystallography on additional pilin subunits, high-resolution electron microscopy reconstructions of intact pilus filaments, and structural biology of additional proteins in the type IV pilus pathway are clearly important next steps for understanding the mechanisms of pilus assembly, retraction, and function.

Citation: Forest K. 2005. Structure and Assembly of Type IV Pilins, p 81-100. In Waksman G, Caparon M, Hultgren S (ed), Structural Biology of Bacterial Pathogenesis. ASM Press, Washington, DC. doi: 10.1128/9781555818395.ch6

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Structure and Assembly of Type IV Pilins

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Figure 1

Pilin structure-based sequence alignment. (a) Sequences of V. cholerae TcpA, N. gonorrhoeae MS11 pilin (GC), P. aeruginosa strain K122-4 pilin, and P. aeruginosa PAK pilin are aligned based on the three-dimensional structures. Sequence identity (grey shading if three of four residues are the same) is evident in the N-terminal half of the boxed α1-helix. Secondary-structure elements below each sequence highlight the structurally conserved β-sheet (solid arrows) and disulfide bond (reverse video). Species-specific β-strands (dashed arrows) and helices (wavy boxes) occur largely in the αβ loop and D-region. Amino acids contributing to species-specific functionalities are in bold italics. TcpA residues involved in crystal packing and fiberstabilizing hydrophobic interactions (Y51, P58, A59, T60, K68, L69, G72, L73, L76, G77, K121, L176, T177, I179, V182, and L185); the MS11 glycosylation site (S63), phosphorylation site (S68), and hypervariable region (residues 128 to 141); the PAK and K122-4 receptorbinding loops (residues 131 to 144); and the K122-4 second disulfide bond (C57 to C93) are shown. (b) Conserved α/β-roll pilin fold, with the locations of species-specific αβ loop and D-region shown schematically.

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Figure 1

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Figure 2

Structure of the N. meningitidis outer membrane secretin PilQ as determined by negative-stain electron microscopy reconstruction with 12–fold averaging. (A) Top-down view showing the central cavity; overall width, 155 Å. (B) Side-on view, rotated 90° about the x axis from panel A; overall height, 120 Å. R and P indicate the ring and plug regions, respectively. Reprinted from Collins et al. (2003) with permission.

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Figure 2

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