Studies on ligand interactions of human complement factor H

The work reported in this thesis is mainly biochemical research on the properties of the human immune system plasma protein, complement factor H (FH). A major function of FH is to bind to “foreign” or “altered-host” surfaces, mainly by recognising charge cluster motifs. When bound to a surface, it down regulates activation of the complement system on that surface. Its binding properties towards a range of other proteins and macromolecules, have been examined, mainly by ELISA-style assays. Research then focused on a smaller number of these FH ligands, which appear to bind FH very strongly, and not, as is the usual situation, by charge interactions. These ligands are Adrenomedullin, Trinitrophenyl-derivatised ligands, and dinitrophenol-derivatised ligands (TNP and DNP). The binding and dissociation characteristics of these ligands have been examined, the binding optimised, and it has been shown that TNP and DNP derivatised ligands can be used for affinity purification of FH from human plasma. A factor H homologue in plasma, C4bp, also binds these ligands, but a number of other FH homologues in plasma do not (eg beta2 glycoprotein1). Expression systems have been obtained from other labs to make recombinant segments of FH and recombinant protein expressed in order to narrow down the binding sites on FH for these ligands. Binding sites in 3 regions of FH have been located, and the effects of ligand binding on the complement-regulatory functions of FH have been assessed.