Bacterial direction: Oxygenated perspective

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  • Published: Jul 1, 2012
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Bacterial direction: Oxygenated perspective

Breathing new life into aerotaxis studies

Time-resolved ultraviolet resonance Raman spectroscopy has been used to reveal the way in which bacteria change direction in response to an oxygen concentration.
Conformational changes in HemAT dimer
Illustration: Samir El-Mashtoly

A small, but potentially very important, study that utilises NMR spectroscopy and other techniques has been used to reveal a possible mechanism that explains why patients with diabetes have a greater risk of developing heart disease.

Time-resolved ultraviolet resonance Raman spectroscopy has been used to reveal the way in which bacteria change direction in response to an oxygen concentration.

Samir El-Mashtoly at the Ruhr-Universitaet Bochum, Germany, working together with researchers at the University of Hyogo and the Okazaki Institute for Integrative Bioscience, Japan, are hoping to explain new details of how single-cell organisms, such as bacteria, can respond to environmental conditions. They have looked at the microbe Bacillus subtilis and investigated the molecular interactions occurring during aerotaxis, the movement of the bacterium towards a raised oxygen concentration. Specifically, their Raman investigations focused on the conformational changes taking place within the bacterial protein HemAT. This protein is an oxygen sensor that sends a command to the flagellar motor which controls the direction of movement of the microbe via a signal transduction pathway.

The team explains that the signal transduction process starts with binding of oxygen to the haem domain of HemAT, the domain is, of course, akin to the oxygen-binding centre in the red blood cell protein haemoglobin but the protein structures are very different. In the former it is the oxygen sensor domain of HemAT. The oxygen binding process leads to a conformational change in this domain, which triggers additional conformational changes within HemAT that ultimately nudges the signalling domain into action. This domain thus alerts the cell to a rise in oxygen concentration, which stimulates the motor of the flagellum to drive the bacterium up the oxygen gradient.

El-Mashtoly and colleagues used the time-resolved ultraviolet resonance Raman spectroscopic facilities in the Picobiology Institute in Japan to take a close look at how the chemical information travels from the sensor domain of HemAT to its signalling domain. The technique allowing them to look at the local environments and hydrogen bonding interactions of the aromatic amino acids on a nanosecond to microsecond timescale.

The team found that the conformational change in the haem sensor domain induces a displacement of two protein helices within HemAT, which influences another helix connected directly to the signalling domain. The conformational cascade therefore converts the process of oxygen binding into an output for the signalling domain of the protein.

"The temporal behaviour of the Raman intensities of the Trp, Tyr, and Phe [amino acid] residues suggests the presence of at least two phases of conformational changes in a time range of nanoseconds to hundreds of microseconds," the team explains. "The increase in the intensity of Trp, Tyr, and Phe bands within hundreds of nanoseconds indicates a displacement of the B- and G-helices, suggesting that the haem structural changes are communicated to specific sites in the sensor domain."

Related Links

J Biol Chem, 2012, online: "Site-specific Protein Dynamics in Communication Pathway from Sensor to Signaling Domain of Oxygen Sensor Protein, HemAT-Bs"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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