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Infection and Immunity, December 2002, p. 6741-6750, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.6741-6750.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Cloning and Porin Activity of the Major Outer Membrane Protein P1 from Coxiella burnetii

Sunita Varghees,1 Kati Kiss,1 Giovanni Frans,1 Orit Braha,2 and James E. Samuel1*

Department of Medical Microbiology and Immunology,1 Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, Texas 77843-11142

Received 30 April 2002/ Returned for modification 18 June 2002/ Accepted 27 August 2002

Coxiella burnetii, the etiological agent of Q fever, is a gram-negative obligate intracellular bacterium. Two striking characteristics of this microorganism are its ability to thrive within a phagolysosome and its ability to persist in the environment outside a host cell. These abilities have been attributed to the existence of C. burnetii developmental cycle variants: large-cell variants (LCV), small-cell variants (SCV), and small dense cells (SDC). Variants differ in protein profiles, including differential expression of a major outer membrane protein (MOMP) of C. burnetii, designated P1. The ~29-kDa MOMP is highly expressed in LCV, down-regulated in SCV, and not apparent in SDC. We sought to characterize P1 through purification of native protein for N-terminal analysis, cloning, and functional studies. Highly purified P1, extracted from C. burnetii membranes by using the zwitterionic detergent Empigen, allowed the determination of N-terminal and internal peptide sequences. The entire P1 coding locus was cloned by PCR amplification based upon these peptide sequences, followed by inverse PCR. Comparison of the predicted P1 amino acid sequences among the C. burnetii isolates Nine Mile, Koka, Scurry, and Kerns indicated a high degree of conservation. Structural prediction suggests that the peptide has a predominantly ß-sheet conformation, consistent with bacterial porins. Typical porin characteristics were observed for native P1, including detergent solubilization properties, heat modification of purified protein, and channel formation in a planar lipid bilayer. Characterization of differentially expressed P1 as a porin increases our understanding of the function of morphological variants and their role in pathogenesis.

* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, 407 Reynolds Medical Building, Texas A&M University System Health Sciences Center, College Station, TX 77843-1114. Phone: (979) 862-1684. Fax: (979) 845-3479. E-mail: jsamuel{at}tamu.edu.

Editor: B. B. Finlay

Infection and Immunity, December 2002, p. 6741-6750, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.6741-6750.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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