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Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

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One enzyme, many faces: urease is also canatoxin.

Carlo Frederico Moro¹, Fábio C S Nogueira², Carlos Gabriel Moreira Almeida¹

¹Graduate Program in Medicine and Health Sciences, Pontificia Universidade Católica do Rio Grande do Sul (PUCRS), Porto Alegre, RS, Brazil.

Journal of Biomolecular Structure & Dynamics

|December 22, 2022

Summary

Canatoxin (CNTX) is an isoform of jack bean urease (JBU). Formaldehyde treatment stabilizes CNTX by modifying amino acids at the hexamer

Keywords:

Formaldehyde amino acid modification oligomerization protein surface stabilization tandem mass spectrometry

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Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

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Area of Science:

Biochemistry
Plant Science
Enzymology

Background:

Ureases are enzymes that hydrolyze urea. Jack bean urease (JBU) is a hexameric protein. Canatoxin (CNTX) is a related neurotoxic protein isolated from jack bean seeds.
CNTX exhibits lower molecular mass and enzyme activity than JBU and tends to form inactive oligomers upon storage.

Purpose of the Study:

To characterize CNTX as an isoform of JBU.
To elucidate the mechanism of CNTX stabilization by formaldehyde treatment.

Main Methods:

Nano-liquid chromatography-tandem mass spectrometry (nano-LC-MS/MS) for peptide analysis.
De novo sequencing to identify amino acid substitutions.
MS/MS analysis of formaldehyde-treated CNTX.

Main Results:

CNTX shares 804 identical amino acids with JBU (840 residues), indicating it is an isoform likely from a paralog gene.
Fifteen peptides with amino acid substitutions were identified in CNTX.
Formaldehyde treatment modified amino acid residues at the trimer-trimer interface of the JBU hexamer structure in CNTX.
Stabilization prevents hexamer formation and aggregation.

Conclusions:

CNTX is confirmed as an isoform of JBU.
Formaldehyde stabilizes CNTX by modifying surface residues at the trimer-trimer interface, preventing oligomerization and preserving toxicity.