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Streptokinase activates plasminogen bound to human group C and G streptococci through M-like proteins
A Ben Nasr1, A Wistedt, U Ringdahl
1Department of Medical and Physiological Chemistry, Lund University, Sweden.
Abstract:
An ability to interact with plasminogen or plasmin could provide micro-organisms with a mechanism for invasion. Thus, group A, C and G streptococci secrete streptokinase which binds and activates plasminogen. Some streptococci also express surface structures which bind plasminogen without causing its activation. Plasminogen-binding surface proteins were extracted from one group C and one group G streptococcal isolate. Both proteins were found to bind plasmin, fibrinogen and serum albumin in addition to plasminogen. Gene fragments encoding the streptococcal proteins were amplified by PCR and were subsequently cloned and expressed in Escherichia coli. DNA sequence determination revealed for both genes open reading frames encoding proteins which contained repetitive domains and a carboxyl-terminal unrepeated region that were typical of M and M-like proteins. Though the amino-terminal regions of the group C and G streptococcal proteins demonstrated a rather high overall similarity between themselves, they were not similar to the variable regions of other M-like proteins with one exception: there was a 46% identity between the first 22 amino acids of the group G streptococcal protein and the corresponding sequence of PAM, the plasminogen-binding M-like protein of type M53 group A streptococci. Like the proteins extracted from the streptococci, the recombinant proteins bound plasminogen, fibrinogen and albumin. The three plasma proteins bound to separate sites on the streptococcal M-like proteins. Plasminogen bound by the group C and G streptococcal proteins was readily activated by streptokinase, providing evidence for a functional link between the secreted plasminogen-activator and proteins exposed on the bacterial surface.
Insights
Streptococcal surface proteins bind human plasminogen and plasma proteins, aiding bacterial invasion. These M-like proteins facilitate plasminogen activation by streptokinase, linking surface structures to secreted activators.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Microbial pathogens utilize host proteins for invasion and survival.
- Streptococci secrete streptokinase to activate plasminogen, a key component of the fibrinolytic system.
- Some streptococci express surface proteins that bind plasminogen without activation.
Purpose of the Study:
- To characterize plasminogen-binding surface proteins from group C and G streptococci.
- To investigate the binding properties and genetic basis of these streptococcal proteins.
- To explore the functional relationship between surface-bound and secreted plasminogen-binding factors.
Main Methods:
- Extraction and purification of plasminogen-binding proteins from streptococcal isolates.
- Polymerase chain reaction (PCR) amplification, cloning, and expression of gene fragments in Escherichia coli.
- DNA sequencing and sequence homology analysis.
- Binding assays with plasminogen, plasmin, fibrinogen, and albumin.
Main Results:
- Extracted and recombinant proteins bound plasminogen, fibrinogen, and albumin.
- Proteins contained repetitive domains and carboxyl-terminal unrepeated regions characteristic of M-like proteins.
- A significant sequence identity was found between the group G protein and PAM, a known plasminogen-binding protein.
- Plasma proteins bound to distinct sites on the streptococcal M-like proteins.
- Bound plasminogen was readily activated by streptokinase.
Conclusions:
- Group C and G streptococcal surface proteins are M-like proteins with broad plasma protein binding capabilities.
- These proteins possess separate binding sites for plasminogen, fibrinogen, and albumin.
- A functional link exists between secreted streptokinase and surface-exposed M-like proteins for plasminogen activation.