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Journal of Bacteriology, March 2007, p. 2063-2068, Vol. 189, No. 5
0021-9193/07/$08.00+0 doi:10.1128/JB.01239-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Departments of Biochemistry & Molecular Biology,1 Microbiology & Immunology, New York Medical College, Valhalla, New York 10595,2 Departments of Medicine,3 Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, Connecticut 060304
Received 7 August 2006/ Accepted 8 December 2006
The outer membrane of Borrelia burgdorferi, the causative agent of Lyme disease, contains very few integral membrane proteins, in contrast to other gram-negative bacteria. BBA74, a Borrelia burgdorferi plasmid-encoded protein, was proposed to be an integral outer membrane protein with putative porin function and designated as a 28-kDa outer membrane-spanning porin (Oms28). In this study, the biophysical properties of BBA74 and its subcellular localization were investigated. BBA74 is posttranslationally modified by signal peptidase I cleavage to a mature 25-kDa protein. The secondary structure of BBA74 as determined by circular dichroism spectroscopy consists of at least 78%
-helix with little ß-sheet structure. BBA74 in intact B. burgdorferi cells was insensitive to proteinase K digestion, and indirect immunofluorescence microscopy showed that BBA74 was not exposed on the cell surface. Triton X-114 extraction of outer membrane vesicle preparations indicated that BBA74 is not an integral membrane protein. Taken together, the data indicate that BBA74 is a periplasmic, outer membrane-associated protein that lacks properties typically associated with porins.
Published ahead of print on 22 December 2006.
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