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Journal of Bacteriology, October 2007, p. 7497-7502, Vol. 189, No. 20
0021-9193/07/$08.00+0     doi:10.1128/JB.00541-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Structure of the Haemophilus influenzae HMW1B Translocator Protein: Evidence for a Twin Pore{triangledown}

Huilin Li,1* Susan Grass,2 Tao Wang,1 Tianbo Liu,3 and Joseph W. St. Geme III2*

Biology Department, Brookhaven National Laboratory, Upton, New York 11973,1 Departments of Pediatrics and Molecular Genetics and Microbiology, Duke University Medical Center, Children's Health Center T901, Durham, North Carolina 27710,2 Department of Chemistry, Lehigh University, 6E Packer Avenue, Bethlehem, Pennsylvania 180153

Received 10 April 2007/ Accepted 1 August 2007

Secretion of the Haemophilus influenzae HMW1 adhesin occurs via the two-partner secretion pathway and requires the HMW1B outer membrane translocator. HMW1B has been subjected to extensive biochemical studies to date. However, direct examination of the structure of HMW1B has been lacking, leaving fundamental questions about the oligomeric state, the membrane-embedded ß-barrel domain, the approximate size of the ß-barrel pore, and the mechanism of translocator activity. In the current study, examination of purified HMW1B by size exclusion chromatography and negative staining electron microscopy revealed that the predominant species was a dimer. In the presence of lipid, purified HMW1B formed two-dimensional crystalline sheets. Examination of these crystals by cryo-electron microscopy allowed determination of a projection structure of HMW1B to 10 Å resolution. The native HMW1B structure is a dimer of ß-barrels, with each ß-barrel measuring 40 Å by 50 Å in the two orthogonal directions and appearing largely occluded, leaving only a narrow pore. These observations suggest that HMW1B undergoes a large conformational change during translocation of the 125-kDa HMW1 adhesin.

* Corresponding author. Mailing address for Huilin Li: Biology Department, Brookhaven National Laboratory, Upton, NY 11973. Phone: (631) 344-2931. Fax: (631) 344-3407. E-mail: hli{at}bnl.gov. Mailing address for Joseph W. St. Geme III: Department of Pediatrics, Duke University Medical Center, 50 Bell Ave. DUMC 3352, Durham, NC 27710. Phone: (919) 681-4080. Fax: (919) 681-2714. E-mail: j.stgeme{at}duke.edu

{triangledown} Published ahead of print on 10 August 2007.

Journal of Bacteriology, October 2007, p. 7497-7502, Vol. 189, No. 20
0021-9193/07/$08.00+0     doi:10.1128/JB.00541-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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