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Related Experiment Video

Updated: Jun 10, 2026

Development of a Negative Selectable Marker for Entamoeba histolytica

Development of a Negative Selectable Marker for Entamoeba histolytica

Published on: December 12, 2010

Giardia lamblia encodes a functional flavohemoglobin.

Steven Rafferty¹, Betty Luu, Raymond E March

¹Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, ON, Canada K9J 7B8. srafferty@trentu.ca

Biochemical and Biophysical Research Communications

|July 27, 2010

Summary

Giardia lamblia possesses a functional flavohemoglobin, a heme protein previously thought absent. This protein likely protects the pathogen from oxygen and nitric oxide, raising new questions about heme acquisition.

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Area of Science:

Molecular Parasitology
Biochemistry
Microbial Pathogenesis

Background:

Giardia lamblia, a mammalian small intestine pathogen, is a facultative anaerobe.
It was previously believed that Giardia lacks heme proteins and a functional respiratory chain.
Genomic analysis revealed putative heme proteins, including one similar to bacterial flavohemoglobins.

Purpose of the Study:

To clone and characterize the functional properties of the Giardia lamblia flavohemoglobin.
To investigate the potential role of this heme protein in Giardia's survival.

Main Methods:

Gene cloning and protein expression for Giardia lamblia flavohemoglobin.
Biochemical assays to determine protein properties, including heme and flavin adenine dinucleotide binding.
Enzyme activity measurements, specifically NADH and NADPH oxidase activity, with and without nitric oxide donors.

Main Results:

The cloned Giardia lamblia flavohemoglobin is a monomeric protein that binds both heme and flavin adenine dinucleotide.
The protein exhibits NADH and NADPH oxidase activity, which is enhanced by nitric oxide.
These properties are consistent with known bacterial flavohemoglobins.

Conclusions:

The Giardia lamblia flavohemoglobin likely functions to protect the parasite against oxidative stress from oxygen and/or nitric oxide.
The presence of a functional heme protein in Giardia necessitates further investigation into its heme acquisition mechanisms.
This finding challenges previous assumptions about Giardia's metabolic capabilities and cofactor requirements.