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Streptococcal C5a peptidase is a highly specific endopeptidase
P P Cleary1, U Prahbu, J B Dale
1Department of Microbiology, University of Minnesota, Minneapolis 55455.
Infection and Immunity
|December 1, 1992
Summary
Streptococcal C5a peptidase (SCPA) cleaves C5a at the His-Lys bond, not Lys-Asp. This specificity suggests SCPA primarily functions to reduce inflammation by eliminating chemotactic signals.
Area of Science:
- Biochemistry
- Immunology
- Microbiology
Background:
- Streptococcal C5a peptidase (SCPA) is an enzyme produced by Streptococcus species.
- The precise cleavage site and function of SCPA in the complement cascade are not fully understood.
- Previous studies suggested SCPA cleaves C5a at a Lys-Asp bond.
Purpose of the Study:
- To determine the exact cleavage site of streptococcal C5a peptidase (SCPA) on C5a.
- To investigate the specificity of SCPA activity.
- To elucidate the functional role of SCPA in the inflammatory response.
Main Methods:
- Compositional analysis of SCPA cleavage products from synthetic C5a peptides.
- Utilized a C5a peptide analog with a modified Lys residue.
- Tested SCPA activity on native C5 protein.
Main Results:
- SCPA specifically cleaves the synthetic C5a peptide at the His-Lys bond, not the previously proposed Lys-Asp bond.
- Cleavage occurs even when Lys is replaced with Gln, confirming His-Lys as the scissile bond.
- Native C5 protein is resistant to SCPA, indicating the His-Lys bond is inaccessible before C5 convertase activation.
Conclusions:
- SCPA exhibits high specificity for C5a, targeting the His-Lys bond.
- The enzyme's primary role is likely to neutralize the chemotactic activity of C5a, thereby reducing inflammation.
- SCPA's function extends beyond simple protein processing for metabolic use.