Site specific mutants of beta-galactosidase show that Tyr-503 is unimportant in Mg2+ binding but that Glu-461 is very important and may be a ligand to Mg2+

Biochemical and Biophysical Research Communications
R A EdwardsR E Huber

Abstract

The Mg2+ concentrations required for half maximal activity, the dissociation constants, and the free energies of binding for Mg2+ bound to wild type beta-galactosidase and several site specific mutants are reported. The mutants have one of the following substitutions: Glu-461 substituted with Asp, Gln, Gly, His, or Lys; or Tyr-503 substituted with Phe, His or Cys. Substitutions for Tyr-503 had little effect on the affinity of the enzyme for Mg2+, implying that Tyr-503 is not involved in Mg2+ binding. Neutrally charged amino acids substituted for the negatively charged Glu-461 significantly decreased the affinity of the enzyme for Mg2+ and substitution of positively charged amino acids at this position further decreased the affinity. On the other hand, substitution by Asp (negative charge) at position 461 had no effect on the binding. Thus, the negatively charged side chain of Glu-461 is important for divalent cation binding to beta-galactosidase.

References

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Citations

Mar 1, 1994·The International Journal of Biochemistry·R E HuberS K Khare
Oct 20, 2005·Journal of Bioscience and Bioengineering·T NakayamaT Nishino
Nov 28, 2006·Biochemical and Biophysical Research Communications·Gopinath SutendraReuben E Huber
May 28, 2009·Protein Science : a Publication of the Protein Society·Douglas H JuersReuben E Huber
Jan 1, 1996·Biochemistry and Cell Biology = Biochimie Et Biologie Cellulaire·M Martinez-Bilbao, R E Huber
Dec 1, 1990·Archives of Biochemistry and Biophysics·M Ring, R E Huber

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