Summary
Studies on β-galactosidase α-complementation are reviewed. The isolation and structure of two β-galactosidase fragments that form an enzymically active complex are described. One of these is a cyanogen bromide peptide from whole β-galactosidase; the other is a dimeric-protein from a lacZ deletion mutant of Escherichia coli. The mechanism most likely involves an initial binding of two cyanogen bromide peptides to the dimer, followed by formation of a tetramer, and finally a slow conformational change of the complex to a native-like enzyme. The overall reaction is essentially irreversible. A region of the polypeptide chain involved in dimer-dimer contact must be supplied by the cyanogen bromide peptide. α-Complemented enzyme contains overlapping sequences. Proteolytic experiments were carried out to determine the origin of the funtionally important segment. The effect on a-complementation of amino acid substitutions at four positions in the polypeptide chain was investigated. The implications of these results for β-galactosidase structure and for proteins in general are discussed.
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Zabin, I. β-Galactosidase α-complementation. Mol Cell Biochem 49, 87–96 (1982). https://doi.org/10.1007/BF00242487
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DOI: https://doi.org/10.1007/BF00242487