COMBINATORIAL PROTEIN LIBRARY SCREENING BY PERIPLASMIC EXPRESSION
First Claim
1. A method of obtaining a bacterium comprising a nucleic acid sequence encoding a binding polypeptide having specific affinity for a target ligand comprising the steps of:
- (a) providing a Gram negative bacterium comprising an inner and an outer membrane and a periplasm, said bacterium expressing a nucleic acid sequence encoding a candidate binding polypeptide, wherein the candidate binding polypeptide is exposed within the periplasm of said bacterium;
(b) contacting the bacterium with a labeled ligand under conditions wherein the labeled ligand is capable of contacting the binding polypeptide; and
(c) selecting said bacterium based on the presence of said labeled ligand bound to said candidate binding polypeptide.
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Abstract
The invention overcomes the deficiencies of the prior art by providing a rapid approach for isolating binding proteins capable of binding small molecules and peptides. In the technique, libraries of candidate binding proteins, such as antibody sequences, are expressed in the periplasm of gram negative bacteria and mixed with a labeled ligand. In clones expressing recombinant polypeptides with affinity for the ligand, the concentration of the labeled ligand bound to the binding protein is increased and allows the cells to be isolated from the rest of the library. Where fluorescent labeling of the target ligand is used, cells may be isolated by fluorescence activated cell sorting (FACS). The approach is more rapid than prior art methods and avoids problems associated with the outer surface-expression of ligand fusion proteins employed with phage display.
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Citations
47 Claims
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1. A method of obtaining a bacterium comprising a nucleic acid sequence encoding a binding polypeptide having specific affinity for a target ligand comprising the steps of:
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(a) providing a Gram negative bacterium comprising an inner and an outer membrane and a periplasm, said bacterium expressing a nucleic acid sequence encoding a candidate binding polypeptide, wherein the candidate binding polypeptide is exposed within the periplasm of said bacterium;
(b) contacting the bacterium with a labeled ligand under conditions wherein the labeled ligand is capable of contacting the binding polypeptide; and
(c) selecting said bacterium based on the presence of said labeled ligand bound to said candidate binding polypeptide. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
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43. A method of obtaining a bacteria comprising a nucleic acid sequence encoding at least a first binding polypeptide having specific affinity for a target ligand comprising the steps of:
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(a) providing a Gram negative bacterium comprising an inner and an outer membrane and a periplasm, said bacteria expressing a nucleic acid sequence encoding a least a candidate binding polypeptide, wherein the candidate binding polypeptide is exposed within the periplasm of said bacterium;
(b) contacting the bacterium with a fluorescently labeled ligand under conditions wherein the labeled ligand is capable of contacting the binding polypeptide; and
(c) selecting said bacterium for the presence of the fluorescently labeled ligand using FACS. - View Dependent Claims (44, 45, 46, 47)
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Specification