Related Experiment Videos
Characterization of hemin binding activity of Streptococcus pneumoniae
1Department of Microbiology, College of Medicine, Howard University, Washington, DC 20059, USA.
Abstract:
Streptococcus pneumoniae is a causative agent of bacterial pneumonia, otitis media, meningitis, and bacteremia. It causes considerable morbidity and mortality throughout the world, especially among children, the elderly, and immunocompromised individuals. We have demonstrated previously that the growth of S. pneumoniae is limited under iron-depleted conditions and can be restored by the addition of either hemin or hemoglobin. In the present study, we showed that S. pneumoniae had the ability to bind hemin and that the level of hemin binding activity was not affected by supplementation of the growth medium with iron. Approximately 70 to 80% of the hemin binding activity was mediated by proteinase-resistant components, and the remainder was mediated by proteins. Hemin binding proteins were located in both soluble extract and envelope fractions of pneumococcal cells. By batch affinity chromatography, a major hemin binding polypeptide with an apparent molecular mass of 43 kDa was identified in the cell lysate of S. pneumoniae. Polyclonal antibodies against this polypeptide were raised. By immunoblot analysis, this hemin binding polypeptide was localized in the envelope and did not exhibit any variation in molecular weight among all serotypes tested. The subcellular distribution of hemin binding activity may have functional implications.
Insights
Streptococcus pneumoniae binds hemin, crucial for growth when iron is scarce. A 43 kDa protein in the bacterial envelope mediates this essential hemin-binding activity.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Streptococcus pneumoniae causes severe infections like pneumonia and meningitis globally.
- Bacterial growth, including S. pneumoniae, is often limited by iron availability.
- Previous studies indicated iron-depleted growth of S. pneumoniae can be restored by hemin or hemoglobin.
Purpose of the Study:
- To investigate the hemin-binding capabilities of Streptococcus pneumoniae.
- To identify and characterize the proteins responsible for hemin binding in S. pneumoniae.
- To determine the location and potential variations of hemin-binding components.
Main Methods:
- Assessing hemin-binding activity in S. pneumoniae under varying iron conditions.
- Utilizing proteinase digestion to differentiate protein and non-protein mediated binding.
- Employing batch affinity chromatography to isolate hemin-binding polypeptides.
- Raising polyclonal antibodies and performing immunoblot analysis for protein localization.
Main Results:
- S. pneumoniae exhibits significant hemin-binding activity, independent of iron supplementation.
- Approximately 70-80% of hemin binding is mediated by proteinase-resistant components, with the remainder attributed to proteins.
- A major 43 kDa hemin-binding polypeptide was identified in the cell lysate and localized to the bacterial envelope.
- This 43 kDa polypeptide showed consistent molecular weight across tested S. pneumoniae serotypes.
Conclusions:
- Streptococcus pneumoniae possesses a robust mechanism for hemin binding, likely vital for acquiring this iron source.
- A conserved 43 kDa envelope protein is a key component of the hemin-binding system in S. pneumoniae.
- The identified hemin-binding protein and its localization suggest functional importance in bacterial physiology and pathogenesis.