Abstract :
[en] he outer membrane of Treponema pallidum, the non-cultivable agent of venereal
syphilis, contains a paucity of protein(s) which has yet to be definitively
identified. In contrast, the outer membranes of gram-negative bacteria contain
abundant immunogenic membrane-spanning beta-barrel proteins mainly involved in
nutrient transport. The absence of orthologs of gram-negative porins and outer
membrane nutrient-specific transporters in the T. pallidum genome predicts that
nutrient transport across the outer membrane must differ fundamentally in T.
pallidum and gram-negative bacteria. Here we describe a T. pallidum outer
membrane protein (TP0453) that, in contrast to all integral outer membrane
proteins of known structure, lacks extensive beta-sheet structure and does not
traverse the outer membrane to become surface exposed. TP0453 is a lipoprotein
with an amphiphilic polypeptide containing multiple membrane-inserting,
amphipathic alpha-helices. Insertion of the recombinant, non-lipidated protein
into artificial membranes results in bilayer destabilization and enhanced
permeability. Our findings lead us to hypothesize that TP0453 is a novel type of
bacterial outer membrane protein which may render the T. pallidum outer membrane
permeable to nutrients while remaining inaccessible to antibody.
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