title: Effects of zinc on factor I cofactor activity of C4b-binding protein and factor H.
abstract: Complement inhibition is to a large extent achieved by proteolytic degradation of activated complement factors C3b and C4b by factor I (FI). This reaction requires a cofactor protein that binds C3b/C4b. We found that the cofactor activity of C4b-binding protein towards C4b/C3b and factor H towards C3b increase at micromolar concentrations of Zn(2+) and are abolished at 2 mM Zn(2+) and above. 65Zn(2+) bound to C3b and C4b molecules but not the cofactors or FI when they were immobilized in a native form on a nitrocellulose membrane. Zn(2+) binding constants for C3met (0.2 microM) and C4met (0.1 microM) were determined using fluorescent chelator. It appears that higher cofactor activity at low zinc concentrations is due to an increase of affinity between C4b/C3b and cofactor proteins as assessed by surface plasmon resonance. Inhibition of the reaction seen at higher concentrations is due to aggregation of C4b/C3b.
authors.affiliation: Department of Clinical Chemistry, Lund University, University Hospital Malmö, S-205 02, Malmö, Sweden. Anna.Blom@klkemi.mas.lu.se
authors.forename: Anna M
authors.initials: AM
authors.lastname: Blom
authors.forename: Lena
authors.initials: L
authors.lastname: Kask
authors.forename: Bala
authors.initials: B
authors.lastname: Ramesh
authors.forename: Andreas
authors.initials: A
authors.lastname: Hillarp
mesh_terms: D000818:Animals; D001798:Blood Proteins; D002478:Cells, Cultured; D050577:Complement C3-C5 Convertases / Q000096:biosynthesis*; D003179:Complement C3b / Q000737:chemistry / Q000378:metabolism; D003180:Complement C3b Inactivator Proteins; D015935:Complement C4b; D017242:Complement Factor H; D003169:Complement Inactivator Proteins; D003171:Complement Pathway, Classical / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D005340:Fibrinogen / Q000737:chemistry / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D012756:Sheep; D015032:Zinc / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D001798:Blood Proteins; D003180:Complement C3b Inactivator Proteins; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D003179:Complement C3b; D015935:Complement C4b; D017242:Complement Factor H; D005340:Fibrinogen; D050577:Complement C3-C5 Convertases; D015032:Zinc