Elucidation of the Substrate Specificity of the C1s Protease of the Classical Complement Pathway

The complement system is a central component of host defense but can also contribute to the inflammation seen in pathological conditions. The C1s protease of the first complement component, the C1 complex, initiates the pathway. In this study we have elucidated the full specificity of the enzyme for...

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Bibliographic Details
Published in:The Journal of biological chemistry 2005-11, Vol.280 (47), p.39510-39514
Main Authors: Kerr, Felicity K., O'Brien, Grace, Quinsey, Noelene S., Whisstock, James C., Boyd, Sarah, de la Banda, Maria Garcia, Kaiserman, Dion, Matthews, Antony Y., Bird, Phillip I., Pike, Robert N.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Base Sequence
Binding Sites - genetics
Catalytic Domain - genetics
Complement C1s - chemistry
Complement C1s - metabolism
Complement Pathway, Classical - physiology
DNA - genetics
Humans
In Vitro Techniques
Models, Molecular
Oligopeptides - chemistry
Oligopeptides - genetics
Oligopeptides - metabolism
Peptide Library
Substrate Specificity
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Summary:The complement system is a central component of host defense but can also contribute to the inflammation seen in pathological conditions. The C1s protease of the first complement component, the C1 complex, initiates the pathway. In this study we have elucidated the full specificity of the enzyme for the first time using a randomized phage display library. It was found that, aside from the crucial P1 position, the S3 and S2 subsites (in that order) played the greatest role in determining specificity. C1s prefers Leu or Val at P3 and Gly or Ala residues at P2. Apart from the S2′ position, which showed specificity for Leu, prime subsites did not greatly affect specificity. It was evident, however, that together they significantly contributed to the efficiency of cleavage of a peptide. A peptide substrate based on the top sequence obtained in the phage display validated these results and produced the best kinetics of any C1s substrate to date. The results allow an understanding of the active site specificity of the C1s protease for the first time and provide a basis for the development of specific inhibitors aimed at controlling inflammation associated with complement activation in adverse pathological situations.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M506131200