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MAp44, a human protein associated with pattern recognition molecules of the complement system and regulating the lectin pathway of complement activation

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  • Department of Medical Biochemistry
  • Department of Medical Microbiology and Immunology
  • Klinisk Immunologi, Aalborg Sygehus
Essential effector functions of innate immunity are mediated by complement activation initiated by soluble pattern recognition molecules: mannan-binding lectin (MBL) and the ficolins. We present a novel, phylogenetically conserved protein, MAp44, which is found in human serum at 1.4 microg/ml in Ca(2+)-dependent complexes with the soluble pattern recognition molecules. The affinity for MBL is in the nanomolar range (K(D) = 0.6 nM) as determined by surface plasmon resonance. The first eight exons of the gene for MAp44 encode four domains shared with MBL-associated serine protease (MASP)-1 and MASP-3 (CUB1-EGF-CUB2-CCP1), and a ninth exon encodes C-terminal 17 aa unique to MAp44. mRNA profiling in human tissues shows high expression in the heart. MAp44 competes with MASP-2 for binding to MBL and ficolins, resulting in inhibition of complement activation. Our results add a novel mechanism to those known to control the innate immune system.
Original languageEnglish
JournalJournal of Immunology
Pages (from-to)7371-8
Number of pages7
Publication statusPublished - 2009

    Research areas

  • Amino Acid Sequence, Animals, Base Sequence, Complement Activation, Electrophoresis, Polyacrylamide Gel, Humans, Isoenzymes, Lectins, Mannose-Binding Lectin, Mannose-Binding Protein-Associated Serine Proteases, Molecular Sequence Data, Phylogeny, RNA, Messenger, Reverse Transcriptase Polymerase Chain Reaction, Surface Plasmon Resonance

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