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Identification of Protein Interacting Partners Using Tandem Affinity Purification
Published on: February 25, 2012
Identification and characterization of a novel secreted immunoglobulin binding protein from group A streptococcus
P K Fagan1, D Reinscheid, B Gottschalk
1Division of Microbiology, GBF-National Research Center for Biotechnology, Braunschweig, Germany.
Abstract:
Immunoglobulin binding proteins are one of several pathogenicity factors which have been associated with invasive disease caused by group A streptococci. The surface-bound M and M-like proteins of Streptococcus pyogenes are the most characterized of these immunoglobulin binding proteins, and in most cases they bind only a single antibody class. Here we report the identification of a novel non-M-type secreted protein, designated SibA (for secreted immunoglobulin binding protein from group A streptococcus), which binds all immunoglobulin G (IgG) subclasses, the Fc and Fab fragments, and also IgA and IgM. SibA has no significant sequence homology to any M-related proteins, is not found in the vir regulon, and contains none of the characteristic M-protein regions, such as the A or C repeats. Like M proteins, however, SibA does have relatively high levels of alanine, lysine, glutamic acid, leucine, and glycine. SibA and M proteins also share an alpha-helical N-terminal secondary structure which has been previously implicated in immunoglobulin binding in M proteins. Evidence presented here indicates that this is also the case for SibA. SibA also has regions of local similarity with other coiled-coil proteins such as Listeria monocytogenes P45 autolysin, human myosin heavy chain, macrogolgin, and Schistoma mansoni paramyosin, some of which are of potential significance since cross-reactive antibodies between myosin proteins and M proteins have been implicated in the development of the autoimmune sequelae of streptococcal disease.
Insights
Researchers discovered a new group A streptococcus protein, SibA, which binds multiple antibody types, unlike previously known M proteins. This finding expands our understanding of streptococcal virulence factors and potential autoimmune links.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Group A Streptococcus (GAS) causes invasive diseases, with immunoglobulin-binding proteins identified as key virulence factors.
- Surface-bound M and M-like proteins of Streptococcus pyogenes are well-characterized but typically bind only one antibody class.
Purpose of the Study:
- To identify and characterize novel immunoglobulin-binding proteins secreted by group A streptococci.
- To investigate the binding capabilities and structural features of the newly identified protein, SibA.
Main Methods:
- Identification and sequencing of the novel secreted protein, SibA.
- Analysis of SibA's binding specificity across various immunoglobulin (Ig) subclasses, Fc and Fab fragments, IgA, and IgM.
- Sequence homology searches and structural analysis, including coiled-coil protein comparisons.
Main Results:
- A novel secreted protein, SibA (secreted immunoglobulin binding protein from group A streptococcus), was identified.
- SibA exhibits broad binding activity, interacting with all immunoglobulin G (IgG) subclasses, Fc and Fab fragments, IgA, and IgM.
- SibA lacks homology to M-related proteins but shares an alpha-helical N-terminal structure with M proteins, suggesting a similar immunoglobulin-binding mechanism.
Conclusions:
- SibA represents a novel class of secreted immunoglobulin-binding proteins in group A streptococcus.
- Its broad antibody-binding capacity suggests a significant role in streptococcal pathogenesis.
- Structural similarities to other coiled-coil proteins hint at potential roles in autoimmune responses, similar to M proteins.
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