Affiliation:
1. Institute of Microbiology and Biotechnology, University of Ulm, 89069 Ulm, Germany
2. University of Applied Sciences Bonn-Rhein-Sieg, 53359 Rheinbach, Germany
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
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