Association of a high-molecular weight arginine-binding protein of Fusobacterium nucleatum ATCC 10953 with adhesion to secretory immunoglobulin A and coaggregation with Streptococcus cristatus.
BACKGROUND
Fusobacterium nucleatum coaggregates with a diverse range of bacterial species, and binds to host tissues and proteins such as immunoglobulin. These interactions may support the attachment of a variety of organisms to oral surfaces and can facilitate the invasion of soft tissues. We hypothesized that coaggregation with streptococci and immunoglobulin binding may occur by a common adhesin sensitive to l-arginine.


METHODS
Repeated mixing of F. nucleatum with non-immune secretory immunoglobulin A (S-IgA) and recovery of non-agglutinating cells isolated a spontaneous mutant (isolate 21) of F. nucleatum that was defective in S-IgA binding. Wild-type and mutant F. nucleatum were compared by coaggregation and adhesion assays.


RESULTS
Isolate 21 exhibited significantly reduced S-IgA binding and coaggregation with oral streptococci but not with Porphyromonas gingivalis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the mutant was deficient compared to wild-type for a single protein of approximately 360 kilodaltons. The corresponding protein was isolated from wild-type F. nucleatum protein preparations by coprecipitation with arginine-agarose beads. This protein was able to bind both Streptococcus cristatus and S-IgA. Mass spectrometry analysis indicated that this protein was closely related to putative autotransporter proteins in other F. nucleatum strains and was a 100% match to the deduced amino acid sequence of a 10,638-base-pair open reading frame in the incomplete genome sequence of F. nucleatum ATCC 10,953. Peptides identified by MS-MS analysis spanned most of the predicted amino acid sequence, suggesting that the mature protein is not subject to postsecretory cleavage.


CONCLUSIONS
Coaggregation represents a novel function within the autotransporter class of proteins, which are often associated with virulence.
Edwards
A M
AM
Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN 55455, USA.
Grossman
T J
TJ
Rudney
J D
JD
D018829:Adhesins, Bacterial / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001120:Arginine / Q000378:metabolism; D001422:Bacterial Adhesion / Q000502:physiology*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D016967:Fusobacterium nucleatum / Q000502:physiology*; D007071:Immunoglobulin A, Secretory / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D034363:Viridans Streptococci / Q000502:physiology*
D018829:Adhesins, Bacterial; D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D007071:Immunoglobulin A, Secretory; D001120:Arginine