In vitro alpha-complementation of beta-galactosidase on a bacteriophage surface

Surface display of large multimeric non-secreted proteins is advantageous on the bacteriophage lambda compared with the widely used filamentous phage systems. A model system, the alpha-complementation of beta-galactosidase, was used for both further general characterization of protein-protein interactions on the lambda tail tube surface and for specifically probing the structure of the phage-displayed beta-galactosidase tetramer. In this complementation system, dimeric enzymatically inactive N-terminal deletion mutants of beta-galactosidase (alpha-accepters) interact with peptides whose sequences span the region of the deletion (alpha-peptides) with the subsequent formation of tetramers and restoration of activity, The lambda phage could tolerate incorporation into their tail tubes of a limited number of copies of V protein (gpV) subunits C-terminally modified with an active alpha-peptide. Purified alpha-peptide phage showed specific in vitro alpha-complementation with an alpha-acceptor extract; the features of this reaction suggested that each complemented monomer can directly associate with an alpha-peptide displayed within the same tail tube structure, In contrast to the alpha-peptide, attempts to surface display an alpha-acceptor protein in a similar manner were unsuccessful. The implications of this work for surface-display cDNA libraries are discussed.