Identification and immunoreactivity of proteins released from Streptococcus agalactiae

Abstract

The aim of the present study was to identify released proteins of Streptococcus agalactiae and to investigate their immunoreactivity with human sera to determine whether such proteins might be viable as carrier proteins in conjugate vaccines. Infections with S. agalactiae are the leading cause of sepsis and meningitis in neonates. Vaccination of women of childbearing age would be a desirable alternative to intrapartum antibiotic prophylaxis, but factors that mediate S. agalactiae invasive disease and virulence are poorly defined. Capsule-based vaccines have shown only low immunogenicity to date, and interest has shifted towards S. agalactiae proteins, either as candidate vaccine antigens or as carrier proteins for serotype-specific S. agalactiae polysaccharides. In this study, some major released proteins of S. agalactiae could be identified, including molecules known to be present on the surface of bacterial cells but not previously described as released proteins, such as CAMP factor, a phosphocarrier protein, aldolase, enolase, PcsB, and heat-shock protein 70. Serotype-specific differences in the protein patterns of extracellular products and immunoreactivity with human sera could be detected by SDS-PAGE and Western blot. The identification of unexpected released proteins may indicate secondary functions for these proteins. In addition, the widespread immunoreactivity of these proteins with human sera as shown by Western blot indicates that released proteins may be promising candidates as carrier proteins in conjugate vaccines.

Release of metabolic enzymes by Giardia in response to interaction with intestinal epithelial cells

“…We were not able to detect any signal sequences in the proteins but now there are many examples of secreted proteins in eukaryotes without signal sequences [35]. Enolase has been implicated in the pathogenesis of other microbes colonizing mucosal surfaces [29,36]; prokaryotic Streptococcus agalactiae, S. sobrinus, S. pyogenes and eukaryotic Candida albicans ␣-enolases are secreted [36,37], while other enolases are surface-associated [29,38,39]. Some of these enolases are immunodominant [29,36], as is Giardia enolase [24,25].…”

Streptococcus agalactiae GAPDH Is a Virulence-Associated Immunomodulatory Protein

“…The K M values obtained were higher (23.8 mM and 32.6 mM, respectively, for F1,6bisP and NAD ϩ ) than the values reported for GAPDH of group A streptococci (33) (1.33 mM for G-3-P and 156.7 M for NAD ϩ ), indicating a weaker affinity of the recombinant GBS enzyme for its substrates. In addition to its presence in the cytosol, GAPDH has also been described as a surface (28,31) or a secreted (36) protein. Consistently, we demonstrated in this study by Western blot and sequencing analysis that NEM316 GAPDH was present in culture supernatants devoid of isocitrate dehydrogenase activity, a cytosolic protein used as a marker of bacterial lysis.…”

“…In GBS, GADPH is localized in their surface and is highly homologous to the plasmin receptor of group A streptococci (35). Although devoid of signal peptide, streptococcal GAPDH has been described as a secreted protein (36,37).…”

Extracellular proteins of Clostridium chauvoei are protective in a mouse model

“…Moreover, sera raised against extracellular antigens also recognised cellular antigens with the same molecular mass (130, 72 and 34 kDa), indicating that the major soluble antigens secreted or in other way released into the culture medium were also present in the cells as somatic antigens. Likewise, S. agalactiae showed an unexpected similarity between cellular and major released immunoreactive proteins, including molecules known to be present on the surface of bacterial cells and not previously described as released proteins (Jacobsson, 2003;Fluegge et al, 2004). These results may indicate secondary functions for the released proteins which can be considered promising vaccine candidates.…”

“…Furthermore, these proteins have been identified as new vaccine candidates due to their ability to induce protective immunity against these pathogenic agents (Strindelius et al, 2002;Fluegge et al, 2004;Cockeran et al, 2005). Extracellular proteins were secreted by C. chauvoei strains mainly in the logarithmic phase and conserved in the early stationary phase, whereas at the late stationary phase several bands diminished or were not detected in strain ATCC 10092 and local strain 17.…”