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Structural stability and heat‐induced conformational change of two complement inhibitors: C4b‐binding protein and factor H
Author(s) -
Kask Lena,
Villoutreix Bruno O.,
Steen Mårten,
Ramesh Bala,
Dahlbäck Björn,
Blom Anna M.
Publication year - 2004
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.03516504
Subject(s) - complement control protein , circular dichroism , chemistry , complement system , biophysics , protein structure , protein secondary structure , conformational change , alternative complement pathway , factor h , biochemistry , crystallography , biology , antibody , immunology
The complement inhibitors C4b‐binding protein (C4BP) and factor H (FH) both consist of complement control protein (CCP) domains. Here we examined the secondary structure of both proteins by circular dichroism and Fourier‐transform infrared technique at temperatures ranging from 30°C–90°C. We found that predominantly β‐sheet structure of both proteins was stable up to 70°C, and that a reversible conformational change toward α‐helix was apparent at temperatures ranging from 70°C to 90°C. The ability of both proteins to inhibit complement was not impaired after incubation at 95°C, exposure to extreme pH conditions, and storage at room temperature for several months. Similar remarkable stability was previously observed for vaccinia virus control protein (VCP), which is also composed of CCP domains; it therefore seems to be a general property of CCP‐containing proteins. A typical CCP domain has a hydrophobic core, which is wrapped in β‐sheets and stabilized by two disulphide bridges. How the CCP domains tolerate harsh conditions is unclear, but it could be due to a combination of high content of prolines, hydrophobic residues, and the presence of two disulphide bridges within each domain. These findings are of interest because CCP‐containing complement inhibitors have been proposed as clinical agents to be used to control unwanted complement activation that contributes to many diseases.