The SrtA Sortase of Streptococcus agalactiae is required for cell wall anchoring of proteins containing the LPXTG motif, for adhesion to epithelial cells, and for colonization of the mouse intestine.
Streptococcus agalactiae (group B streptococcus [GBS]) is the leading cause of neonatal pneumonia, sepsis, and meningitis. An in silico genome analysis indicated that GBS strain NEM316 encodes 35 proteins containing an LPXTG motif which are thought to be covalently linked to the peptidoglycan by an enzyme called sortase. The role of these cell wall-anchored proteins in GBS pathogenesis was evaluated on a global level by inactivating the srtA gene. This gene encodes the major sortase SrtA that anchors most of the LPXTG-containing proteins. We chose the C5a peptidase (ScpB) and Alp2, an abundant immunogenic protein, as prototypical LPXTG-containing proteins. As expected, the SrtA knockout mutant was unable to anchor the C5a peptidase (ScpB) and Alp2 to the cell wall. Complementation with plasmid-borne srtA inserted into the chromosome restored the correct surface localization of both ScpB and Alp2. Interestingly, the SrtA mutant was impaired for binding to the major extracellular matrix components fibronectin and fibrinogen and displayed a significant reduction in adherence to human (A549, HeLa, and Caco-2) and murine (L2) epithelial cells compared to the parental wild-type strain. Surprisingly, the inactivation of srtA had no effect on the virulence of the type III strain of GBS in a neonatal rat model (measured by the 50% lethal dose and lung colonization) but strongly impaired the capacity of the strain to colonize the intestines of gnotobiotic mice in a competition assay. These results demonstrate that LPXTG-containing proteins are involved in cell adhesion and GBS persistence in vivo.
Lalioui
Lila
L
Unité de Biologie des Bactéries Pathogènes à Gram-Positif, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris, France.
Pellegrini
Elisabeth
E
Dramsi
Shaynoor
S
Baptista
Marina
M
Bourgeois
Nadege
N
Doucet-Populaire
Florence
F
Rusniok
Christophe
C
Zouine
Mohamed
M
Glaser
Philippe
P
Kunst
Frank
F
Poyart
Claire
C
Trieu-Cuot
Patrick
P
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D004847:Epithelial Cells / Q000382:microbiology; D005353:Fibronectins / Q000502:physiology; D006801:Humans; D007422:Intestines / Q000382:microbiology*; D051379:Mice; D008809:Mice, Inbred C3H; D008969:Molecular Sequence Data; D051381:Rats; D017207:Rats, Sprague-Dawley; D013292:Streptococcus agalactiae / Q000502:physiology*
D001426:Bacterial Proteins; D005353:Fibronectins; D019881:Aminoacyltransferases; C120542:sortase A; D003546:Cysteine Endopeptidases