The surface protein Srr-1 of Streptococcus agalactiae binds human keratin 4 and promotes adherence to epithelial HEp-2 cells.
Streptococcus agalactiae is frequently the cause of bacterial sepsis and meningitis in neonates. In addition, it is a commensal bacterium that colonizes the mammalian gastrointestinal tract. During its commensal and pathogenic lifestyles, S. agalactiae colonizes and invades a number of host compartments, thereby interacting with different host proteins. In the present study, the serine-rich repeat protein Srr-1 from S. agalactiae was functionally investigated. Immunofluorescence microscopy showed that Srr-1 was localized on the surface of streptococcal cells. The Srr-1 protein was shown to interact with a 62-kDa protein in human saliva, which was identified by matrix-assisted laser desorption ionization-time-of-flight analysis as human keratin 4 (K4). Immunoblot and enzyme-linked immunosorbent assay experiments allowed us to narrow down the K4 binding domain in Srr-1 to a region of 157 amino acids (aa). Furthermore, the Srr-1 binding domain of K4 was identified in the C-terminal 255 aa of human K4. Deletion of the srr-1 gene in the genome of S. agalactiae revealed that this gene plays a role in bacterial binding to human K4 and that it is involved in adherence to epithelial HEp-2 cells. Binding to immobilized K4 and adherence to HEp-2 cells were restored by introducing the srr-1 gene on a shuttle plasmid into the srr-1 mutant. Furthermore, incubation of HEp-2 cells with the K4 binding domain of Srr-1 blocked S. agalactiae adherence to epithelial cells in a dose-dependent fashion. This is the first report describing the interaction of a bacterial protein with human K4.
Samen
Ulrike
U
Division of Gene Therapy, University of Ulm, 89081 Ulm, Germany. u.samen@gmx.de
Eikmanns
Bernhard J
BJ
Reinscheid
Dieter J
DJ
Borges
Frédéric
F
D018829:Adhesins, Bacterial / Q000235:genetics / Q000378:metabolism*; D001422:Bacterial Adhesion / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000382:microbiology*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D006801:Humans; D015151:Immunoblotting; D053527:Keratin-4 / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D011387:Prokaryotic Cells / Q000737:chemistry; D011485:Protein Binding; D025941:Protein Interaction Mapping; D012463:Saliva / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013292:Streptococcus agalactiae / Q000235:genetics / Q000502:physiology*
D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D053527:Keratin-4; D008565:Membrane Proteins; C524542:Srr-1 protein, Streptococcus agalactiae
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