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Related Experiment Videos

Substrate recognition by "password" in p-hydroxybenzoate hydroxylase

B A Palfey1, G R Moran, B Entsch

  • 1Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA. brupalf@umich.edu

Biochemistry
|February 4, 1999
PubMed
Summary

p-hydroxybenzoate hydroxylase (PHBH) uses a novel mechanism where substrate deprotonation triggers flavin movement. This ensures the enzyme only proceeds with suitable aromatic substrates, optimizing the catalytic cycle.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Molecular Recognition

Background:

  • p-hydroxybenzoate hydroxylase (PHBH) is an enzyme known to exist in two flavin conformations.
  • Flavin movement within PHBH is crucial for its catalytic activity.

Purpose of the Study:

  • To investigate the conformational changes of the flavin in PHBH.
  • To elucidate the role of substrate binding and deprotonation in flavin movement.
  • To understand the mechanism of molecular recognition in PHBH.

Main Methods:

  • Kinetic studies to observe flavin movement upon NADPH binding.
  • pH dependence studies on wild-type PHBH and a His72Asn mutant to assess substrate deprotonation effects.

Main Results:

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  • NADPH binding induces flavin movement from a buried to an exposed conformation.
  • Substrate deprotonation, facilitated by an internal proton transport network, is essential for flavin movement.
  • The His72Asn mutation affects the pH dependence, highlighting the role of specific residues.

Conclusions:

  • Flavin movement in PHBH is directly linked to substrate deprotonation.
  • This linkage represents a novel molecular recognition mechanism, ensuring enzyme commitment to suitable substrates.
  • The findings provide new insights into enzyme catalytic cycles and substrate specificity.