A hemerythrin-like domain in a bacterial chemotaxis protein

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Hemerythrin (Hr) is an oxygen-carrying protein in marine invertebrates with a characteristic diiron active site.
• A novel Hr-like sequence motif was identified in the gene dcrH of Desulfovibrio (D.) vulgaris, an anaerobic bacterium.

Purpose of the Study:

• To characterize the Hr-like domain found in D. vulgaris DcrH.
• To investigate the structure and function of this novel microbial Hr-like protein.

Main Methods:

• Sequence analysis to identify the Hr-like motif in dcrH.
• Immunoblotting to confirm expression of full-length DcrH in D. vulgaris.
• Recombinant expression and purification of the DcrH C-terminal domain (DcrH-Hr).
• Spectroscopic analysis (UV-vis absorption, resonance Raman) to study the active site and oxygen binding.

Main Results:

• The DcrH-Hr protein folds into a stable structure with an oxo-bridged diiron(III) site similar to Hr.
• DcrH-Hr forms an oxygen adduct upon exposure to air, also resembling Hr.
• The oxygen adduct of DcrH-Hr is autoxidized rapidly at room temperature, and its oxygen binding pocket appears larger than Hr's.
• DcrH-Hr is the first characterized hemerythrin-like protein from a microorganism.

Conclusions:

• The Hr-like domain in D. vulgaris DcrH exhibits functional and structural similarities to hemerythrin.
• The increased air sensitivity and potential larger binding pocket suggest a role in oxygen sensing for DcrH in its native anaerobic environment.
• This finding expands the known diversity of hemerythrin-like proteins to the microbial world.