title: Borrelia burgdorferi BBA74, a periplasmic protein associated with the outer membrane, lacks porin-like properties.
abstract: 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% alpha-helix with little beta-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.
authors.affiliation: Department of Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA.
authors.forename: Vishwaroop
authors.initials: V
authors.lastname: Mulay
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Caimano
authors.forename: Dionysios
authors.initials: D
authors.lastname: Liveris
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Desrosiers
authors.forename: Justin D
authors.initials: JD
authors.lastname: Radolf
authors.forename: Ira
authors.initials: I
authors.lastname: Schwartz
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000032:analysis / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology; D019084:Fluorescent Antibody Technique, Indirect; D033903:Periplasmic Proteins / Q000032:analysis / Q000737:chemistry*; D018272:Porins / Q000737:chemistry* / Q000502:physiology; D017433:Protein Structure, Secondary
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D033903:Periplasmic Proteins; D018272:Porins; C100895:protein Oms28, Borrelia burgdorferi