Cell surface display, screening and production of proteins of interest

1. A method of displaying a polypeptide of interest on a host cell, the method comprising:

a. providing a host cell comprising a first nucleic acid encoding an engineered protein,

wherein the host cell expresses a recombinant biotin protein ligase covalently fused to a first secretion leader peptide,

wherein the host cell is a eukaryotic host cell,

wherein the first secretion leader peptide is fused to the N-terminus of the recombinant biotin protein ligase,

wherein the host cell has avidin, streptavidin or variant thereof capable of binding biotin, coupled to the extracellular side of the host cell surface,

wherein the engineered protein comprises a polypeptide of interest covalently fused to a second secretion leader peptide,

wherein the second secretion leader peptide is at the N-terminus of the engineered protein,

wherein the first secretion leader peptide and the second secretion leader peptide is a peptide that directs proteins to the eukaryotic secretory pathway,

wherein the engineered protein comprises a first biotin acceptor peptide covalently fused to either the N-terminus or C-terminus of the polypeptide of interest,

wherein the first biotin acceptor peptide contains a lysine residue, wherein the ε-amino group of the lysine residue is capable of forming a post-translational amide-linkage to the carboxyl group of biotin when catalyzed by the recombinant biotin protein ligase,

wherein the recombinant biotin protein ligase is selected from the group of SEQ ID NOs 1-11 and variants thereof capable of catalyzing the post-translational linkage between biotin and the first biotin acceptor peptide, and

b. expressing the engineered protein, wherein expression of the engineered protein results in intracellular coupling of a biotin moiety covalently to the first biotin acceptor peptide catalyzed by the recombinant biotin protein ligase within the host cell secretory pathway and in secretion of the biotinylated engineered protein without the secretion leader peptide from the cell surface into the extracellular medium so that the biotin moiety of the engineered protein binds noncovalently and specifically to the avidin, streptavidin, or variant thereof capable of binding biotin,

thereby displaying the polypeptide of interest on the extracellular side of the host cell surface.

2. The method of claim 1 , wherein the host cell is a yeast cell.

3. The method of claim 2 , wherein the extracellular side of the host cell surface is a yeast cell wall.

4. The method of claim 1 , wherein the polypeptide of interest comprises an antibody, a single chain antibody, a scaffold protein, or a fragment thereof.

5. The method of claim 4 , wherein the first biotin acceptor peptide is covalently fused to the C-terminus of the constant region of the antibody.

6. The method of claim 1 , further comprising the step of evaluating a property of the polypeptide of interest displayed on the extracellular side of the host cell surface.

7. The method of claim 1 , comprising displaying a plurality of different polypeptides of interest, wherein each different polypeptide of interest is encoded by a different first nucleic acid in a different host cell.

8. The method of claim 7 , wherein the different polypeptides of interest are sequence variants of each other.

9. The method of claim 1 , further comprising isolating a polypeptide of interest having a predetermined function or level of activity.

10. The method of claim 1 , wherein the avidin, streptavidin or variant thereof capable of binding biotin is coupled to the extracellular side of the host cell surface by conjugation to the extracellular side of the cell surface.

11. The method of claim 1 , wherein step (a) further comprises coupling biotin to the extracellular side of the host cell surface followed by incubating the host cell with avidin, streptavidin or variant thereof capable of binding biotin.

12. The method of claim 11 , wherein the coupling biotin to the extracellular side of the host cell surface is done by in vitro biotinylating the extracellular side of the host cell surface.

13. The method of claim 11 , wherein the coupling biotin to the extracellular side of the host cell surface is done by in vivo biotinylating the extracellular side of the host cell surface.

14. The method of claim 13 , wherein the host cell further comprises a second nucleic acid encoding an engineered cell surface protein,

wherein the engineered cell surface protein comprises a cell surface protein covalently fused to a third secretion leader peptide,

wherein the third secretion leader peptide is at the N-terminus of the engineered cell surface protein,

wherein the third secretion leader peptide is a peptide that directs proteins to the eukaryotic secretory pathway,

wherein the engineered protein comprises a second biotin acceptor peptide covalently fused to either the N-terminus or C-terminus of the cell surface protein,

wherein the second biotin acceptor peptide contains a lysine residue, wherein the ε-amino group of the lysine residue is capable of forming a post-translational amide-linkage to the carboxyl group of biotin when catalyzed by the recombinant biotin protein ligase,

wherein the recombinant biotin protein ligase is selected from the group of SEQ ID NOs 1-11 and variants thereof capable of catalyzing the post-translational linkage between biotin and the second biotin acceptor peptide, and

expressing the engineered cell surface protein, wherein expression of the engineered cell surface protein results in intracellular coupling of a biotin moiety covalently to the second biotin acceptor peptide catalyzed by the recombinant biotin protein ligase within the host cell secretory pathway and in transporting the biotinylated engineered cell surface protein to the extracellular side of the host cell surface,

thereby displaying the biotinylated engineered cell surface protein on the extracellular side of the host cell surface.

15. The method of claim 14 , wherein the cell surface protein is a yeast cell wall protein.

16. The method of claim 14 , wherein the third secretion leader peptide is the naturally occurring secretion leader peptide of the cell surface protein.

17. The method of claim 1 , wherein the host cell further comprises a second nucleic acid encoding an engineered cell surface protein,

wherein the engineered cell surface protein comprises a cell surface protein covalently fused to a third secretion leader peptide,

wherein the cell surface protein comprises avidin, streptavidin or variant thereof capable of binding biotin,

wherein the engineered cell surface protein comprises an anchoring motif,

wherein the third secretion leader peptide is at the N-terminus of the engineered cell surface protein,

wherein the third secretion leader peptide is a peptide that directs proteins to the eukaryotic secretory pathway,

wherein the avidin, streptavidin or variant thereof capable of binding biotin is fused to the N-terminus of the anchoring motif, and

expressing the engineered cell surface protein, wherein expression of the engineered cell surface protein results in transporting the engineered cell surface protein to the extracellular side of the host cell surface,

thereby displaying the avidin, streptavidin or variant thereof capable of binding biotin on the extracellular side of the host cell surface.

18. The method of claim 17 , wherein the anchoring motif is selected from the group consisting of GPI anchor, modified GPI anchor, alpha-agglutinin, flocculation protein, a major cell wall protein, CCW14, CIS3, CWP1, PIR1, and PIR3.

19. The method of claim 17 , wherein the third secretion leader peptide is the naturally occurring secretion leader peptide of the anchoring motif.