Beta-galactosidase

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Some interesting facts [1]

  • A tetramer of 4 identical subunits
  • Each subunit is 120kD.
  • Active only as a tetramer.
  • Mutations in some of the codons of the N-terminal 60aa or C-terminal 100aa results in an inactive, dimeric β-galactosidase. [2]
  • If the above sequences are deleted, the missing protein fragment can be replaced by the corresponding peptide. This is called intracistronic alpha or omega complementation respectively.
  • Its N-terminal 23 residues can be replaced by any amino acid residues without affecting the enzymatic activity.
  • A mutant with an internal deletion of codons 21-41 of the lacZ gene does not produce any active β-galactosidase.
  • A mutant with a deletion of everything past residue 60 (i.e. it expresses only the first 60 N-terminal amino acids) does not produce any active β-galactosidase.

Reference

  1. ISBN:3-11-014830-7 [Muller-Hill-1996]
  2. ISBN:0317118099 [Beckwith-1970]
  3. Ullmann A. Complementation in beta-galactosidase: from protein structure to genetic engineering. Bioessays. 1992 Mar;14(3):201-5. DOI:10.1002/bies.950140311 | PubMed ID:1345751 | HubMed [Ullmann-Bioessays-1992]