Borrelia burgdorferi lipoproteins are secreted to the outer surface by default.
Borrelia spirochaetes are unique among diderm bacteria in their abundance of surface-displayed lipoproteins, some of which play important roles in the pathogenesis of Lyme disease and relapsing fever. To identify the lipoprotein-sorting signals in Borrelia burgdorferi, we generated chimeras between the outer surface lipoprotein OspA, the periplasmic oligopeptide-binding lipoprotein OppAIV and mRFP1, a monomeric red fluorescent reporter protein. Localization of OspA and OppAIV point mutants showed that Borrelia lipoproteins do not follow the '+2' sorting rule which targets lipoproteins to the cytoplasmic or outer membrane of Gram-negative bacteria via the Lol pathway. Fusions of mRFP1 to short N-terminal lipopeptides of OspA, and surprisingly OppAIV, were targeted to the spirochaetal surface. Mutagenesis of the OspA N-terminus defined less than five N-terminal amino acids as the minimal secretion-facilitating signal. With the exception of negative charges, which can act as partial subsurface retention signals in certain peptide contexts, lipoprotein secretion occurs independent of N-terminal sequence. Together, these data indicate that Borrelia lipoproteins are targeted to the bacterial surface by default, but can be retained in the periplasm by sequence-specific signals.
Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Mail Stop 3029, 3901 Rainbow Boulevard, Kansas City, 66160, USA.
Ryan J
RJ
Schulze
Wolfram R
WR
Zückert
D000595:Amino Acid Sequence; D000954:Antigens, Surface / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001428:Bacterial Vaccines; D025065:Borrelia burgdorferi / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D000097573:Red Fluorescent Protein
D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D002352:Carrier Proteins; D008074:Lipoproteins; D008164:Luminescent Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D000097573:Red Fluorescent Protein; C072045:OspA protein; C046506:oligopeptide-binding protein, bacteria