Crystal structure and functional characterization of the complement regulator mannose-binding lectin (MBL)/ficolin-associated protein-1 (MAP-1)

Mikkel Ole Skjoedt, Pietro Roversi, Tina Hummelshøj, Yaseelan Palarasah, Anne Rosbjerg, Steven Johnson, Susan M. Lea, Peter Garred

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32 Citations (Scopus)


The human lectin complement pathway activation molecules comprise mannose-binding lectin (MBL) and ficolin-1, -2, and -3 in complex with associated serine proteases MASP-1, -2, and -3 and the non-enzymatic small MBL associated protein or sMAP. Recently, a novel plasma protein named MBL/ficolin-associated protein-1 (MAP-1) was identified in humans. This protein is the result of a differential splicing of the MASP1 gene and includes the major part of the heavy chain but lacks the serine protease domain. We investigated the direct interactions of MAP-1 and MASP-3 with ficolin-3 and MBL using surface plasmon resonance and found affinities around 5 nM and 2.5 nM, respectively. We studied structural aspects of MAP-1 and could show by multi-angle laser light scattering that MAP-1 forms a calcium-dependent homodimer in solution. We were able to determine the crystal structure of MAP-1, which also contains a head-to-tail dimer ∼146 Å long. This structure of MAP-1 also enables modeling and assembly of the MASP-1 molecule in its entirety. Finally we found that MAP-1 competes with all three MASPs for ligand binding and is able to mediate a strong dose-dependent inhibitory effect on the lectin pathway activation, as measured by levels of C3 and C9.

Original languageEnglish
Pages (from-to)32913-32921
Number of pages9
JournalJournal of Biological Chemistry
Issue number39
Publication statusPublished - 21 Sept 2012
Externally publishedYes

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