Related Experiment Videos
Evidence for actinlike proteins in an M protein-negative strain of Streptococcus pyogenes
1Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
Abstract:
Antigens shared between Streptococcus pyogenes and heart tissue may play an important role in autoimmune cardiac injury associated with acute rheumatic fever. Antiheart/antistreptococcal antibodies found in the disease react with antigens of S. pyogenes, including M protein and a 60-kDa antigen distinct from M protein. Heart antigens recognized by these cross-reactive antistreptococcal antibodies include myosin and actin. To investigate the presence of a streptococcal actin, established protocols for the polymerization and isolation of eukaryotic actin were used to extract and concentrate actinlike proteins from M- streptococcal cells. The polymerized bacterial actin from the streptococcal extract was probed in immunoblots with an antiactin monoclonal antibody. Two proteins of about 60 kDa in the polymerized bacterial actin reacted with the antiactin antibody. Proteins in the polymerized bacterial actin extract of about 43 and 60 kDa behaved like eukaryotic actin by binding to myosin and DNase I affinity columns. Filaments were demonstrated by electron microscopy in the polymerized bacterial actinlike extract, which also enhanced the ATPase activity of eukaryotic myosin. The data suggest that proteins resembling actin are present in S. pyogenes.
Insights
Streptococcus pyogenes may possess actin-like proteins, potentially explaining autoimmune reactions in rheumatic fever. These bacterial proteins mimic human actin, reacting with antibodies targeting heart tissue.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Autoimmune cardiac injury in acute rheumatic fever is linked to shared antigens between Streptococcus pyogenes and heart tissue.
- Cross-reactive antibodies in rheumatic fever target both S. pyogenes antigens (M protein, 60-kDa antigen) and heart components like myosin and actin.
Purpose of the Study:
- To investigate the presence and characteristics of actin-like proteins in Streptococcus pyogenes.
- To determine if S. pyogenes contains proteins that mimic eukaryotic actin and could contribute to autoimmune responses.
Main Methods:
- Utilized established protocols for eukaryotic actin polymerization and isolation to extract proteins from S. pyogenes.
- Employed immunoblots with antiactin monoclonal antibodies to detect actin-like proteins.
- Assessed protein behavior using myosin and DNase I affinity chromatography.
- Performed electron microscopy to visualize protein filaments.
- Measured enhancement of eukaryotic myosin ATPase activity.
Main Results:
- Two proteins of approximately 60 kDa in the polymerized bacterial extract reacted with an antiactin antibody.
- Proteins of 43 kDa and 60 kDa from the extract exhibited actin-like behavior, binding to myosin and DNase I affinity columns.
- Electron microscopy revealed filament formation in the bacterial extract.
- The bacterial extract enhanced the ATPase activity of eukaryotic myosin.
Conclusions:
- The study provides evidence for the presence of actin-like proteins in Streptococcus pyogenes.
- These findings suggest a potential mechanism for molecular mimicry, where bacterial actin-like proteins could trigger autoimmune responses against heart tissue in rheumatic fever.