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Published on: December 19, 2020
Purification of native alpha-enolase from Streptococcus pneumoniae that binds plasminogen and is immunogenic
G C Whiting1, J T Evans1, S Patel1
1Department of Medical Microbiology, Royal Free and University College Medical School, London NW3 2PF.
Abstract:
Many pathogenic bacteria express plasminogen receptors on their surface, which may play a role in the dissemination of organisms by binding plasminogen that, when converted to plasmin, can digest extracellular matrix proteins. A 45-kDa protein was purified from Streptococcus pneumoniae and confirmed as an alpha-enolase by its ability to catalyse the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate and by N-terminal sequencing. The activity of alpha-enolase was found in the cytoplasm and in whole cells. Activity was also demonstrated in cell wall fractions, which confirmed that alpha-enolase is a cytoplasmic antigen also expressed on the surface of S. pneumoniae. The plasminogen-binding activity of alpha-enolase was examined by Western blot, which showed that purified alpha-enolase was able to bind human plasminogen. Immunoblots of the purified 45-kDa alpha-enolase with 22 sera from patients with pneumococcal disease showed binding in 15 cases, indicating that pneumococcal enolase is immunogenic.
Insights
Streptococcus pneumoniae expresses alpha-enolase on its surface, which binds plasminogen. This finding suggests a role for pneumococcal enolase in bacterial dissemination and highlights its immunogenic potential in disease.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Pathogenic bacteria utilize surface receptors to bind host plasminogen, aiding dissemination by facilitating extracellular matrix degradation.
- Streptococcus pneumoniae is a significant human pathogen where such mechanisms are actively investigated.
Purpose of the Study:
- To identify and characterize plasminogen-binding proteins on Streptococcus pneumoniae.
- To investigate the role of alpha-enolase as a surface-expressed plasminogen receptor in S. pneumoniae.
Main Methods:
- Protein purification and biochemical characterization (catalytic activity assay, N-terminal sequencing).
- Subcellular localization studies (cytoplasmic, whole cell, and cell wall fractions).
- Western blot analysis for plasminogen binding and immunogenicity assessment using patient sera.
Main Results:
- A 45-kDa alpha-enolase was purified from S. pneumoniae and confirmed by its enzymatic activity and N-terminal sequence.
- Alpha-enolase exhibited enzymatic activity in the cytoplasm and was detected in cell wall fractions, indicating surface expression.
- Purified alpha-enolase demonstrated direct binding to human plasminogen.
- Fifteen out of 22 sera from patients with pneumococcal disease recognized the purified pneumococcal enolase, confirming its immunogenicity.
Conclusions:
- Streptococcus pneumoniae expresses alpha-enolase on its surface, functioning as a plasminogen-binding protein.
- Surface-expressed alpha-enolase may contribute to S. pneumoniae pathogenesis by facilitating host matrix degradation.
- Pneumococcal enolase is an immunogenic antigen, suggesting its potential as a target for diagnostics or therapeutics.
