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J. Biochem, 2003, Vol. 133, No. 2 231-237
© 2003 Japanese Biochemical Society

BIOCHEMISTRY

Characterization of Complement C3 as a Glycyrrhizin (GL)-Binding Protein and the Phosphorylation of C3{alpha} by CK-2, Which Is Potently Inhibited by GL and Glycyrrhetinic Acid In Vitro

Fumitaka Kawakami, Yoshihito Shimoyama and Kenzo Ohtsuki+,

Genetical Biochemistry and Signal Biology, Graduate School of Medical Sciences, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555

The physiological interaction between glycyrrhizin (GL) and serum complement C3, and the inhibitory effects of GL, glycyrrhetinic acid (GA), and a GA derivative (oGA) on the phosphorylation of C3 by casein kinase 2 (CK-2), were investigated in vitro. C3 was found to be a GL-binding protein (gbP), because (i) of its high affinity for a GL-affinity HPLC column; and (ii) both GL and GA induce conformational changes in C3. At least four trypsin-resistant fragments (p30, p25, p18, and p15) were detected when the 32P-labeled C3{alpha} was digested with trypsin in the presence of 100 µM GA. Two of these (p25 and p15) were immuno-precipitated with anti-C3a serum. Furthermore, it was found that C3a contains GL-binding domains, because (i) C3a (anaphylatoxin) could be selectively purified from the synovial fluids of patients with rheumatoid arthritis by GL-affinity column chromatography (HPLC); and (ii) purified human C3a has a high affinity for a GL-affinity column. In addition, C3{alpha} (p115) of C3 was effectively phosphorylated by CK-2 in the presence of poly-Arg (a CK-2 activator) in vitro. This phosphorylation was completely inhibited by 10 µM oGA, 30 µM GA, or 100 µM GL. Taken together, these results suggest that the GL-induced inhibition of the physiological activities of C3a and C3{alpha} may be involved in the anti-inflammatory effect of GL in vivo.

+ To whom correspondence should be addressed. Tel/Fax: +81-42-778-8863, E-mail: ken{at}kitasato-u.ac.jp


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