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Journal of Bacteriology, October 2009, p. 6253-6261, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00563-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Investigation of the Three-Dimensional Architecture of the Collagen Adhesin EmaA of Aggregatibacter actinomycetemcomitans by Electron Tomography{triangledown} ,{dagger}

Chunxiao Yu,1 Keith P. Mintz,1 and Teresa Ruiz2*

Department of Microbiology and Molecular Genetics,1 Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 054052

Received 28 April 2009/ Accepted 3 August 2009

The periodontal pathogen Aggregatibacter actinomycetemcomitans displays on the bacterial surface a nonfimbrial adhesin, EmaA, which is required for collagen binding. In this study, electron tomography was used to characterize the three-dimensional (3D) architecture of this adhesin. The antenna-like surface appendages, corresponding to EmaA, were found to be composed of an ellipsoidal domain capping a rod-like domain that adopts either a straight or a bent conformation at various positions along the length. The most common flexible point along the length of the EmaA appendage was localized 29.4 nm away from the distal end. One-fifth of the appendages were straight and the remaining showed angles distributed between 140° and 170° at this location. Deletion analysis mapped this bend to amino acids 611 to 640 of the protein sequence. The 3D structure of the collagen binding domain of EmaA was generated by alignment and averaging of 9 subvolumes of the adhesin extracted from tomograms. The structure contains three subdomains: a globular structure with a diameter of ~5 nm and a cylindrical domain (~4.4 nm by 5.8 nm) separated by a linker region with a diameter of ~3 nm, followed by a cylindrical domain (~4.6 nm by 6.6 nm). This is the first 3D structure of a trimeric autotransporter protein of A. actinomycetemcomitans.

* Corresponding author. Mailing address: Department of Molecular Physiology and Biophysics, University of Vermont, Rm. 106, HSRF Building, 149 Beaumont Ave., Burlington, VT 05405. Phone: (802) 656-4835. Fax: (802) 656-0747. E-mail: Teresa.Ruiz{at}uvm.edu

{triangledown} Published ahead of print on 28 August 2009.

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

Journal of Bacteriology, October 2009, p. 6253-6261, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00563-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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