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Related Experiment Video

Updated: Jun 16, 2026

Transmembrane Domain Oligomerization Propensity determined by ToxR Assay

Transmembrane Domain Oligomerization Propensity determined by ToxR Assay

Published on: May 26, 2011

Nox4 B-loop creates an interface between the transmembrane and dehydrogenase domains.

Heather M Jackson¹, Tsukasa Kawahara, Yukio Nisimoto

¹Department of Pathology and Experimental Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.

The Journal of Biological Chemistry

|February 9, 2010

Summary

The cytosolic B-loop in NADPH oxidase (Nox) enzymes is crucial for Nox4 activity, binding to the dehydrogenase domain to mediate interactions between enzyme domains and regulate function.

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Area of Science:

Biochemistry
Molecular Biology
Enzymology

Background:

NADPH oxidase (Nox) enzymes link reactive oxygen species to physiological processes by targeting redox-sensitive amino acids.
The cytosolic B-loop, a conserved region in Nox1-4, contains a polybasic region important for Nox2 activity and subunit assembly.
Conservation of the B-loop in Nox4, which lacks p47(phox)/p67(phox) dependency, suggests an additional role in Nox function.

Purpose of the Study:

To investigate the functional importance of the Nox4 B-loop in enzyme activity and subunit interactions.
To determine the binding site and characteristics of the interaction between the Nox4 B-loop and its target domain.

Main Methods:

Site-directed mutagenesis of Nox4 B-loop residues to assess effects on enzyme activity.
Fluorescence polarization assays to quantify the binding affinity between Nox4 B-loop peptides and the dehydrogenase domain.
Dehydrogenase domain truncations to map the B-loop binding site.

Main Results:

Mutations in the Nox4 B-loop significantly decreased holo-Nox4 activity.
The Nox4 B-loop peptide bound to the Nox4 dehydrogenase domain with a dissociation constant (K(d)) of 58 +/- 12 nm.
The binding site was localized to the N-terminal half of the NADPH-binding subdomain, and the interaction depended on the B-loop's polybasic region, similar to Nox2.

Conclusions:

The B-loop is critical for Nox4 enzymatic activity.
The B-loop interacts with the dehydrogenase domain, suggesting it acts as an interface between transmembrane and dehydrogenase domains in Nox enzymes.
This interaction mechanism is conserved across different Nox enzyme subtypes.