Crystal Structure and Functional Characterization of the Complement Regulator Mannose-binding Lectin (MBL)/Ficolin-associated Protein-1 (MAP-1)

Abstract

Background: MAP-1 is a novel member of the lectin complement pathway. Results: We present the crystal structure of MAP-1 and show that it inhibits central complement factors and interacts with MBL and ficolin at nM affinities. Conclusion: MAP-1 is a Ca 2ϩ -dependent homo-dimer molecule and a key complement regulator. Significance: Structural and functional knowledge of MAP-1 provide important insight to the biology of the complement system.

Heterocomplex Formation between MBL/Ficolin/CL-11–Associated Serine Protease-1 and -3 and MBL/Ficolin/CL-11–Associated Protein-1

“…In comparison, we used the same setup for heterocomplexes preincubated with 10 mM EDTA for 2 h, which caused the middle peak to vanish, suggesting that the heterocomplexes were dissociated. The homodimers were also dissociated into monomers in the presence of EDTA, and this calcium-dependent dimerization of MAP-1 and the MASPs is in agreement with previous notations (14,16,17,19).…”

“…However, MAP-1 comprises the H chain domains that mediate both homodimerization and MBL/ficolin binding similar to the other MASPs (12)(13)(14)(15)(16). In line with this, we have previously shown that MAP-1 can outcompete the MASPs for MBL and ficolin-3 binding (11,14), and in the current study, we questioned the capability of MAP-1 to heterodimerize with the other MASPs. This would shed new light on the mechanism of MAP-1 inhibition, but also on the configuration of the LCP activation complex, where the possible existence of MASP heterodimers has not been firmly established.…”

“…In-house produced mAbs used in the following assays were: anti-MASP-1/-3 mAb F3-46 (14), anti-MAP-1 mAb 20C4 (10), anti-MASP-3 mAb 7D8, and anti-MASP-1/-3/MAP-1 mAb 8B3 (19), anti-ficolin-1 mAb FCN166 (20) anti-ficolin-2 mAbs FCN216 and FCN219 (21), and anti-ficolin-3 mAb FCN334 (22). Moreover, we used the following commercial Abs: anti-MASP-1 polyclonal Ab (pAb) (C-20, sc-50839; Santa Cruz Biotechnology, Heidelberg, Germany), anti-ficolin-1 pAb (HP9039; Hycult Biotech, Uden, The Netherlands), anti-MBL mAbs (HYB 131-10 and 131-11; Bioporto Diagnotics, Gentofte, Denmark), and finally, anti-CL-11 pAb (antiCOLEC-11, 15269-1-AP; Proteintech, Manchester, U.K.).…”

Multiple roles of complement MASP-1 at the interface of innate immune response and coagulation

“…MAp19 is composed of the CUB1-EGF domains of MASP-2 plus 4 unique C-terminal residues, while MAp44 has a domain sequence of CUB1-EGF-CUB2-CCP1 (identical with the MASP-1/3 domains) plus it has 17 unique C-terminal residues. Both proteins have the capacity to dimerize Skjoedt et al, 2012) and interact with the pattern recognition molecules analogously with MASPs. Probably the best quality structure is the 2.3 Å resolution structure of MASP-1/3 CUB1-EGF-CUB2 fragment, which clearly shows Ca 2+ ions bound to all three domains.…”

“…The relevance of this heterodimer formation in vivo is not yet known. Based on the structure of MASP-1/3 Nterminal fragment (Teillet et al, 2008), that of MAp44 (Skjoedt et al, 2012), and the structure of MASP-1 C-terminal fragment ) a model of full length MASP-1 dimer is presented in Fig. 2A. …”