Screening for the effects of complement protein changes

A surface bound protein complex comprising:

• a. a Complement C3b protein or variant thereof, or Complement C4b protein or a variant thereof,
• b. a mutated Complement Factor I protein or variant thereof, and
• c. a Complement Factor I co-factor protein,
• wherein the Complement Factor I protein or variant thereof comprises at least one mutation that results in an inactivation or reduction of Complement Factor I protease activity.

A method for determining the presence, absence or characteristics of a binding event associated with a protein complex, the protein complex comprising a mutant Complement Factor I protein or variant thereof, wherein the protein complex further comprises at least one of the following proteins:

• k. a Complement C3b protein or variant thereof, or Complement C4b protein or a variant thereof, and
• l. a Complement factor I cofactor protein,
• wherein the Complement Factor I protein or variant thereof comprises at least one mutation that reduces or inactivates Complement Factor I protein protease activity of the Complement Factor I protein, wherein the method comprises:
• i) forming said protein complex;
• and
• ii) detecting the presence, absence and/or characteristics of a signal produced by a binding event associated with the formation of said protein complex, wherein said signal is produced by interaction of said Complement Factor I with said Complement C3b or variant thereof, or Complement C4b protein, and said Complement Factor I cofactor protein.

A method for determining the presence, absence, or characteristics of a ligand binding event associated with a protein complex comprising a mutant Complement Factor I protein or variant thereof, wherein the protein complex further comprises at least one of the following proteins;

• m. a Complement C3b protein or variant thereof, or Complement C4b protein or a variant thereof, and
• n. a Complement Factor I cofactor protein,
• wherein the Complement factor I or variant thereof comprises at least one mutation that reduces or inactivates Complement Factor I protease activity of the Complement Factor I protein, and wherein the method comprises;
• i) forming said protein complex, and
• ii) contacting said protein complex with a candidate ligand molecule;
• and
• iii) detecting the presence, absence, and/or characteristics of a signal generated by an interaction of said ligand molecule with said protein complex.