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

TY - JOUR

T1 - Heterocomplex Formation between MBL/Ficolin/CL-11–Associated Serine Protease-1 and -3 and MBL/Ficolin/CL-11–Associated Protein-1

AU - Rosbjerg, Anne

AU - Munthe-Fog, Lea

AU - Garred, Peter

AU - Skjoedt, Mikkel-Ole

PY - 2014/5/1

Y1 - 2014/5/1

N2 - The activity of the complement system is tightly controlled by many fluid-phase and tissue-bound regulators. Mannose-binding lectin (MBL)/ficolin/collectin-11-associated protein-1 (MAP-1) is a recently discovered plasma protein that acts as an upstream inhibitor of the lectin complement pathway (LCP). It has previously been shown that MAP-1 can compete with the MBL/ficolin/ collectin-11-associated serine proteases (MASPs) in binding to MBL and the ficolins. However, this mechanism may only partly explain the inhibitory complement effect of MAP-1. We hypothesized that MAP-1 is also involved in heterocomplex formation with the MASPs thereby breaking the stoichiometry of the activation complexes of the LCP, which could represent an alternative mechanism of MAP-1-mediated complement inhibition. We assessed the heterocomplex formation with ELISA, size-exclusion chromatography, and immunoblotting using both recombinant proteins and serum/plasma. We found that rMAP-1 can engage in heterocomplexes with rMASP-1 and rMASP-3 in a calcium-dependent manner. Moreover, we discovered that rMASP-1 and rMASP-3 also form heterocomplexes under these conditions. Complexes containing both MAP-1 and MASP-1 or -3 were detected in normal human serum and plasma, and depletion of the LCP recognition molecules from ficolin-3-deficient human serum showed that free circulating heterocomplexes also exist in the blood, although the major part appears to be associated with the LCP recognition molecules. Altogether, these findings suggest that MASPs can associate in various combinations and bring new perspectives to the complexity of lectin pathway-driven complement activation. The Journal of Immunology, 2014, 192: 4352-4360.

AB - The activity of the complement system is tightly controlled by many fluid-phase and tissue-bound regulators. Mannose-binding lectin (MBL)/ficolin/collectin-11-associated protein-1 (MAP-1) is a recently discovered plasma protein that acts as an upstream inhibitor of the lectin complement pathway (LCP). It has previously been shown that MAP-1 can compete with the MBL/ficolin/ collectin-11-associated serine proteases (MASPs) in binding to MBL and the ficolins. However, this mechanism may only partly explain the inhibitory complement effect of MAP-1. We hypothesized that MAP-1 is also involved in heterocomplex formation with the MASPs thereby breaking the stoichiometry of the activation complexes of the LCP, which could represent an alternative mechanism of MAP-1-mediated complement inhibition. We assessed the heterocomplex formation with ELISA, size-exclusion chromatography, and immunoblotting using both recombinant proteins and serum/plasma. We found that rMAP-1 can engage in heterocomplexes with rMASP-1 and rMASP-3 in a calcium-dependent manner. Moreover, we discovered that rMASP-1 and rMASP-3 also form heterocomplexes under these conditions. Complexes containing both MAP-1 and MASP-1 or -3 were detected in normal human serum and plasma, and depletion of the LCP recognition molecules from ficolin-3-deficient human serum showed that free circulating heterocomplexes also exist in the blood, although the major part appears to be associated with the LCP recognition molecules. Altogether, these findings suggest that MASPs can associate in various combinations and bring new perspectives to the complexity of lectin pathway-driven complement activation. The Journal of Immunology, 2014, 192: 4352-4360.

KW - Animals

KW - Blotting, Western

KW - CHO Cells

KW - Coculture Techniques

KW - Complement Activation

KW - Complement Pathway, Mannose-Binding Lectin

KW - Cricetinae

KW - Cricetulus

KW - Enzyme-Linked Immunosorbent Assay

KW - Humans

KW - Lectins

KW - Mannose-Binding Lectins

KW - Mannose-Binding Protein-Associated Serine Proteases

KW - Recombinant Proteins

KW - Transfection

U2 - 10.4049/jimmunol.1303263

DO - 10.4049/jimmunol.1303263

M3 - Journal article

C2 - 24683193

SN - 0022-1767

VL - 192

SP - 4352

EP - 4360

JO - Journal of Immunology

JF - Journal of Immunology

IS - 9

ER -