title: Heterogeneity of MBL-MASP complexes.
abstract: In order to study aspects of the stoichiometry and composition of human MBL-MASP complexes in the population, MBL-MASP complexes were bound from sera of 152 healthy individuals onto mannan-coated microtitre plates. Bound mannan-binding lectin (MBL) was measured by ELISA, and the enzyme activities of MBL-bound MASP-1 and MASP-2 were measured by an amidolytic assay and a C4 fixation assay, respectively. MASP-1 activity correlated with MBL concentration, as did MASP-2 activity (in both cases: p<0.0001). This is expected since MASP-1 and MASP-2 are bound to the mannan via MBL. However, when MASP activities were normalised to MBL concentration (i.e. MASP-1 activity/[MBL], MASP-2 activity/[MBL]) MASP-1 activity was inversely correlated with MASP-2. This means on average that high MASP-1 correlates with low MASP-2 and vice-versa, and confirms the hypothesis that native MBL-MASP complexes on average do not have fixed MBL-(MASP-1)-(MASP-2) stoichiometry. The findings are consistent with separate populations of MBL-MASP-1 complexes and MBL-MASP-2 complexes, the concentrations of which show wide inter-individual variation.
authors.affiliation: MRC Immunochemistry Unit, Department of Biochemistry, Oxford University, South Parks Roads, Oxford OX1 3QU, UK.
authors.forename: Karine R
authors.initials: KR
authors.lastname: Mayilyan
authors.forename: Julia S
authors.initials: JS
authors.lastname: Presanis
authors.forename: James N
authors.initials: JN
authors.lastname: Arnold
authors.forename: Krishnan
authors.initials: K
authors.lastname: Hajela
authors.forename: Robert B
authors.initials: RB
authors.lastname: Sim
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D037601:Mannose-Binding Lectin / Q000097:blood / Q000737:chemistry / Q000378:metabolism*; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding
chemical_list: D037601:Mannose-Binding Lectin; D046912:Multiprotein Complexes; D050606:Mannose-Binding Protein-Associated Serine Proteases