Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 106, Issue 10, Pages 3692-3697Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0704048106
Keywords
ligand binding proteins; protein folding quality control; signal peptide; twin-arginine translocation; 2-hybrid system
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Funding
- National Science Foundation [CBET-0449080]
- National Institutes of Health [CA132223A]
- New York State Office of Science, Technology
- Academic Research James D. Watson Award
- Thai Royal Government Fellowship
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We have developed a reliable genetic selection strategy for isolating interacting proteins based on the hitchhiker'' mechanism of the Escherichia coli twin-arginine translocation (Tat) pathway. This method, designated FLI-TRAP (functional ligand-binding identification by Tat-based recognition of associating proteins), is based on the unique ability of the Tat system to efficiently cotranslocate noncovalent complexes of 2 folded polypeptides. In the FLI-TRAP assay, the protein to be screened for interactions is engineered with an N-terminal Tat signal peptide, whereas the known or putative partner protein is fused to mature TEM-1 beta-lactamase (Bla). Using a series of c-Jun and c-Fos leucine zipper (JunLZ and FosLZ) variants of known affinities, we observed that only those chimeras that expressed well and interacted strongly in the cytoplasm were able to colocalize Bla into the periplasm and confer beta-lactam antibiotic resistance to cells. Likewise, the assay was able to efficiently detect interactions between intracellular single-chain Fv (scFv) antibodies and their cognate antigens. The utility of FLI-TRAP was then demonstrated through random library selections of amino acid substitutions that restored (i) heterodimerization to a noninteracting FosLZ variant, and (ii) antigen binding to a low-affinity scFv antibody. Because Tat substrates must be correctly folded before transport, FLI-TRAP favors the identification of soluble, nonaggregating, protease-resistant protein pairs and, thus, provides a powerful tool for routine selection of interacting partners (e. g., antibody-antigen), without the need for purification or immobilization of the binding target.
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