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Cytochrome b5 from Giardia lamblia.

Samiah Alam¹, Janet Yee, Manon Couture

¹Environmental and Life Sciences Graduate Program, Trent University, Peterborough, ON, Canada.

Metallomics : Integrated Biometal Science

|November 16, 2012

Summary

Giardia lamblia, an intestinal parasite, possesses cytochrome b5 proteins despite lacking mitochondria and heme synthesis. This suggests uncharacterized metabolic processes in this medically significant organism.

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Area of Science:

Biochemistry
Parasitology
Molecular Biology

Background:

Giardia lamblia lacks mitochondria and heme synthesis pathways.
The parasite encodes multiple putative heme-binding proteins, including cytochrome b5 family members.

Purpose of the Study:

To characterize a cloned cytochrome b5 protein (gCYTb5-I) from Giardia lamblia.
To investigate the structural and functional properties of gCYTb5-I.

Main Methods:

Cloning and expression of gCYTb5-I in Escherichia coli.
Spectroscopic analysis (UV-visible, resonance Raman) of the purified protein.
Homology modeling to predict protein structure.
Determination of reduction potential.

Main Results:

gCYTb5-I was expressed as a soluble holoprotein.
Spectra and homology modeling indicated a structure similar to microsomal cytochrome b5, with histidine ligands.
The reduction potential of gCYTb5-I (-165 mV vs. SHE) is lower than typical values.
Highly charged flanking sequences of Giardia cytochromes b5 differ from other family members.
A variant lacking these sequences also bound heme.

Conclusions:

Giardia lamblia possesses at least one functional cytochrome b5 (gCYTb5-I) and likely two others.
The unique flanking sequences may influence protein function or localization.
The presence of cytochromes b5 indicates uncharacterized metabolic pathways in Giardia lamblia.