Rational engineering of a minimized immune inhibitor with unique triple-targeting properties

J Immunol. 2013 Jun 1;190(11):5712-21. doi: 10.4049/jimmunol.1203548. Epub 2013 Apr 24.


Inadequate control of the complement system is the underlying or aggravating factor in many human diseases. Whereas treatment options that specifically target the alternative pathway (AP) of complement activation are considered highly desirable, no such option is available in the clinic. In this study, we present a successful example of protein engineering, guided by structural insight on the complement regulator factor H (FH), yielding a novel complement-targeted therapeutic (mini-FH) with clinical potential. Despite a 70% reduction in size, mini-FH retained and in some respects exceeded the regulatory activity and cell surface-recognition properties of its parent protein FH, including the recently described recognition of sites of oxidative stress. Importantly, the chosen design extended the functional spectrum of the inhibitor, as mini-FH showed increased binding to the surface-bound opsonins iC3b and C3dg when compared with FH. Thus, mini-FH is equipped with a unique and clinically valuable triple-targeting profile toward diseased host cells, through its binding to sites of ongoing complement activation, markers of oxidative damage, and host surface-specific polyanions. When assessed in a clinically relevant AP-mediated disease model of paroxysmal nocturnal hemoglobinuria, mini-FH largely outperformed FH and indicated advantages over clinically evaluated AP inhibitors. Thus, the rational engineering of a streamlined FH construct not only provided insight into the function of a key complement regulator, but also yielded a novel inhibitor that combines a triple-targeting approach with high AP-specific inhibitory activity (IC50 ~ 40 nM), which may pave the way toward new options for the treatment of complement-mediated diseases.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Sequence
  • Complement Activation / drug effects
  • Complement Activation / immunology
  • Complement C3b / metabolism
  • Complement Factor H / chemistry*
  • Complement Factor H / metabolism
  • Complement Factor H / pharmacology
  • Complement Pathway, Alternative / drug effects
  • Complement System Proteins / drug effects
  • Complement System Proteins / immunology
  • Complement System Proteins / metabolism
  • Hemolysis / drug effects
  • Hemolysis / immunology
  • Humans
  • Immunologic Factors / chemistry*
  • Immunologic Factors / metabolism
  • Immunologic Factors / pharmacology
  • Molecular Sequence Data
  • Peptide Fragments / metabolism
  • Protein Binding / immunology
  • Protein Engineering*
  • Recombinant Fusion Proteins


  • Immunologic Factors
  • Peptide Fragments
  • Recombinant Fusion Proteins
  • complement C3d,g
  • Complement C3b
  • Complement Factor H
  • Complement System Proteins