Protein/solubility folding assessed by structural complementation

A method for screening protein folding and/or solubility mutants comprising:

• a) providing a gene encoding fusion protein comprising (i) a protein of interest and (ii) a first segment of a marker protein, wherein said first segment does not affect the folding or solubility of the protein of interest,, wherein said fusion protein is not properly folded and/or soluble when expressed in said host cell;
• b) mutagenizing that portion of the gene encoding said protein of interest;
• c) expressing said fusion protein in a host cell that expresses a second segment of said marker protein, wherein said second segment is capable of structural complementation with said first segment;
• and
• d) determining structural complementation,
• wherein a relative increase in structural complementation, as compared to the structural complementation observed with the unmutagenized fusion protein, indicates an increase in proper folding and/or solubility of said protein.

A method for screening candidate modulator substance that modulates protein folding and/or solubility comprising:

• a) providing an expression construct comprising (i) a gene encoding fusion protein, said fusion protein comprising a protein of interest fused to a first segment of a marker protein, wherein said first segment does not affect the folding or solubility of the protein of interest, and (ii) a promoter active in said host cell and operably linked to said gene;
• b) expressing said fusion protein in a host cell that expresses a second segment of said marker protein, wherein said second segment is capable of structural complementation with said first segment;
• c) contacting the host cell with said candidate modulator substance;
• and
• d) determining structural complementation,
• wherein a relative change in structural complementation, as compared to the structural complementation observed in the absence of said candidate modulator substance, indicates that said candidate modulator substance is a modulator of protein folding and/or solubility.