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Characterization of Xenopus laevis complement factor I structure--conservation of modular structure except for an
L M Kunnath-Muglia1, G H Chang, R B Sim
1Department of Hematology/Oncology, Children's Hospital, Boston, MA 02115.
Abstract:
Factor I (C3b/C4b inactivator) is a regulatory protein of the classical and alternative complement pathways. In this paper, we report the sequence of Xenopus factor I cDNA and the deduced protein structure. The basic structure of human preprofactor I, NH2-heavy chain-cleavage peptide-light chain-COOH, is conserved in the frog. However, the frog heavy chain contains a highly charged segment of 29 amino acids, encoded by a poly dA-rich mRNA insert, which is not found in human factor I. The modular structure of the frog heavy chain was analyzed, and found to differ vis-à-vis previously published analyses of human factor I. We also evaluate the timing of factor I transcription during frog embryogenesis.