title: Crystal structure and functional characterization of the complement regulator mannose-binding lectin (MBL)/ficolin-associated protein-1 (MAP-1).
abstract: 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.
authors.affiliation: Laboratory of Molecular Medicine, Department of Clinical Immunology, Rigshospitalet, Faculty of Health Sciences, University of Copenhagen, DK 2100 Copenhagen, Denmark. moskjoedt@gmail.com
authors.forename: Mikkel-Ole
authors.initials: MO
authors.lastname: Skjoedt
authors.forename: Pietro
authors.initials: P
authors.lastname: Roversi
authors.forename: Tina
authors.initials: T
authors.lastname: Hummelshøj
authors.forename: Yaseelan
authors.initials: Y
authors.lastname: Palarasah
authors.forename: Anne
authors.initials: A
authors.lastname: Rosbjerg
authors.forename: Steven
authors.initials: S
authors.lastname: Johnson
authors.forename: Susan M
authors.initials: SM
authors.lastname: Lea
authors.forename: Peter
authors.initials: P
authors.lastname: Garred
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000818:Animals; D016466:CHO Cells; D003176:Complement C3 / Q000737:chemistry / Q000378:metabolism; D003186:Complement C9 / Q000737:chemistry / Q000378:metabolism; D037582:Complement Pathway, Mannose-Binding Lectin / Q000502:physiology*; D006224:Cricetinae; D003412:Cricetulus; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D037102:Lectins / Q000737:chemistry / Q000378:metabolism; D037601:Mannose-Binding Lectin / Q000737:chemistry / Q000378:metabolism; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D055503:Protein Multimerization / Q000502:physiology*; D017433:Protein Structure, Secondary
chemical_list: D003176:Complement C3; D003186:Complement C9; C109662:FCN3 protein, human; D006023:Glycoproteins; D037102:Lectins; D037601:Mannose-Binding Lectin; C084067:MASP1 protein, human; D050606:Mannose-Binding Protein-Associated Serine Proteases