Characterization of Helicobacter pylori γ-glutamyltranspeptidase reveals the molecular basis for substrate specificity and a critical role for the tyrosine 433-containing loop in catalysis

Amy L. Morrow, Kristin Williams, Aaron Sand, Gina Boanca, Joseph J. Barycki

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Helicobacter pylori γ-glutamyltranspeptidase (HpGT) is a member of the N-terminal nucleophile hydrolase superfamily. It is translated as an inactive 60 kDa polypeptide precursor that undergoes intramolecular autocatalytic cleavage to generate a fully active heterodimer composed of a 40 kDa and a 20 kDa subunit. The resultant N-terminus, Thr 380, has been shown to be the catalytic nucleophile in both autoprocessing and enzymatic reactions. Once processed, HpGT catalyzes the hydrolysis of the γ-glutamyl bond in glutathione and its conjugates. To facilitate the determination of physiologically relevant substrates for the enzyme, crystal structures of HpGT in complex with glutamate (1.6 Å, Rfactor = 16.7%, R free = 19.0%) and an inactive HpGT mutant, T380A, in complex with S-(nitrobenzyl)glutathione (1.55 Å, Rfactor = 18.7%, R free = 21.8%) have been determined. Residues that comprise the γ-glutamyl binding site are primarily located in the 20 kDa subunit and make numerous hydrogen bonds with the α-amino and α-carboxylate groups of the substrate. In contrast, a single hydrogen bond occurs between the T380A mutant and the remainder of the ligand. Lack of specific coordination beyond the γ-glutamyl moiety may account for the substrate binding permissiveness of the enzyme. Structural analysis was combined with site-directed mutagenesis of residues involved in maintaining the conformation of a loop region that covers the γ-glutamyl binding site. Results provide evidence that access to this buried site may occur through conformational changes in the Tyr 433-containing loop, as disruption of the intricate hydrogen-bond network responsible for optimal placement of Tyr 433 significantly diminishes catalytic activity.

Original languageEnglish (US)
Pages (from-to)13407-13414
Number of pages8
JournalBiochemistry
Volume46
Issue number46
DOIs
StatePublished - Nov 20 2007

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Substrate Specificity
Catalysis
Helicobacter pylori
Tyrosine
Hydrogen bonds
Hydrogen
Glutathione
Substrates
Binding Sites
Mutagenesis
Nucleophiles
Permissiveness
Enzymes
Structural analysis
Conformations
Glutamic Acid
Hydrolysis
Catalyst activity
Ataxia
Site-Directed Mutagenesis

ASJC Scopus subject areas

  • Biochemistry

Cite this

Characterization of Helicobacter pylori γ-glutamyltranspeptidase reveals the molecular basis for substrate specificity and a critical role for the tyrosine 433-containing loop in catalysis. / Morrow, Amy L.; Williams, Kristin; Sand, Aaron; Boanca, Gina; Barycki, Joseph J.

In: Biochemistry, Vol. 46, No. 46, 20.11.2007, p. 13407-13414.

Research output: Contribution to journalArticle

Morrow, Amy L. ; Williams, Kristin ; Sand, Aaron ; Boanca, Gina ; Barycki, Joseph J. / Characterization of Helicobacter pylori γ-glutamyltranspeptidase reveals the molecular basis for substrate specificity and a critical role for the tyrosine 433-containing loop in catalysis. In: Biochemistry. 2007 ; Vol. 46, No. 46. pp. 13407-13414.
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abstract = "Helicobacter pylori γ-glutamyltranspeptidase (HpGT) is a member of the N-terminal nucleophile hydrolase superfamily. It is translated as an inactive 60 kDa polypeptide precursor that undergoes intramolecular autocatalytic cleavage to generate a fully active heterodimer composed of a 40 kDa and a 20 kDa subunit. The resultant N-terminus, Thr 380, has been shown to be the catalytic nucleophile in both autoprocessing and enzymatic reactions. Once processed, HpGT catalyzes the hydrolysis of the γ-glutamyl bond in glutathione and its conjugates. To facilitate the determination of physiologically relevant substrates for the enzyme, crystal structures of HpGT in complex with glutamate (1.6 {\AA}, Rfactor = 16.7{\%}, R free = 19.0{\%}) and an inactive HpGT mutant, T380A, in complex with S-(nitrobenzyl)glutathione (1.55 {\AA}, Rfactor = 18.7{\%}, R free = 21.8{\%}) have been determined. Residues that comprise the γ-glutamyl binding site are primarily located in the 20 kDa subunit and make numerous hydrogen bonds with the α-amino and α-carboxylate groups of the substrate. In contrast, a single hydrogen bond occurs between the T380A mutant and the remainder of the ligand. Lack of specific coordination beyond the γ-glutamyl moiety may account for the substrate binding permissiveness of the enzyme. Structural analysis was combined with site-directed mutagenesis of residues involved in maintaining the conformation of a loop region that covers the γ-glutamyl binding site. Results provide evidence that access to this buried site may occur through conformational changes in the Tyr 433-containing loop, as disruption of the intricate hydrogen-bond network responsible for optimal placement of Tyr 433 significantly diminishes catalytic activity.",
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