What are examples of thermophilic organisms

Unusual protein structures make bacteria resistant to heat

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03/10/13 Heat protection protein of a particularly thermophilic bacterium clarified

Thermotoga maritima is a bacterium that has adapted very well to growth in hot springs and volcanic rock

At permanent temperatures of more than 80 degrees Celsius, most of the organisms living on earth have no chance of survival. Thermotoga maritima however, it is a bacterium that has adapted very well to growth in hot springs and volcanic rock. In order for bacteria to be able to live under these conditions, their proteins must be very temperature-stable. The increased stability of the protein NusG Thermotoga maritima for example, can be explained by the unusual interplay of individual structural elements. A research team headed by Prof. Dr. Paul Rösch, Chair of Biopolymers at the University of Bayreuth.

Fig. 1: Left: The NusG protein shows no interaction between the N-terminal domain (blue) and the C-terminal domain (red) in bacteria such as Escherichia coli. The domains can move freely relative to one another and can thus bind to other proteins. // Middle: The Escherichia coli bacterium also has a protein similar to NusG, RfaH. Here the domains are close together, they are only opened by the binding of a specific piece of DNA, with the C-terminal domain completely changing its structure. Right: In the bacterium Thermotoga maritima, the interaction between the N-terminal domain (blue) and the C-terminal domain (red) contributes significantly to the stability of the protein. In addition, there is another structural unit (yellow), the function of which is not yet known.
Source: Kristian Schweimer, Chair of Biopolymers, University of Bayreuth

Inoperative, but stable: NusG molecules when closed

As far as is known, proteins of the bacterial NusG type assume vital control functions in many organisms. NusG proteins play a crucial role in gene expression, especially in the process of transcription, in which the genetic information contained in DNA is transcribed into RNA. Here NusG has the task of linking various other proteins with the enzyme RNA polymerase. NusG often consists of two clearly distinguishable spatially structured units, the amino- and the carboxy-terminal domain. As has been observed in previous research, these domains do not come into contact with one another in many bacterial species. This ensures that they do not hinder each other in fulfilling their specific functions.

The situation is different with the type of bacteria Thermotoga maritima. As the Bayreuth scientists, together with colleagues at Freie Universität Berlin and Columbia University, New York, discovered that the NusG protein in these bacteria usually has a closed structure, which means that the two domains are almost always close to one another. As a result, precisely those areas that can interact with other proteins cover each other. In this structure, neither of the two domains is able to take part in vital processes of gene expression. The protein NusG therefore makes itself inoperable, a condition that research calls autoinhibition. And yet this structure has a major advantage for the bacterium: it increases the stability of the protein and enables it to withstand high temperatures.

Lightning-fast structure changes: oscillating NusG molecules

However, NusG does not remain in this protected structure. In order to be able to become active at least for a short time, the protein opens up. Now the two domains have the freedom of movement they need to interact with other proteins. Using NMR spectroscopic analyzes at the University of Bayreuth, the researchers have succeeded in observing this structural change. Their research has led to the result that each NusG molecule opens for the tiny period of 2 hundred thousandths of a second. After that, it immediately reverts to the closed state, in which it remains for about 1 thousandth of a second. Since this relapse into inactivity occurs faster than opening, around 98 percent of the NusG molecules contained in the bacterium are in the closed state at any given point in time. Only the remaining 2 percent are open.

"The constant oscillation between two different structures is an extremely unusual trick of nature, which ensures that the NusG molecules can withstand very high temperatures on the one hand, but can also contribute to gene expression and other cellular processes on the other," explains Dr. Kristian Schweimer from the Department of Biopolymers at the University of Bayreuth. "Such a lightning-fast structural change has not yet been observed in similar proteins from bacteria living at room temperature."

NusG proteins from heat-resistant bacteria: Inactive in normal bacteria

What happens if E. coli bacteria, which live best at body temperature, are divided between these NusG proteins, which oscillate between an open and a closed structure? As the Bayreuth scientists found out, the implanted proteins behave completely passively. “The tendency towards autoinhibition is apparently the reason why the NusG proteins in common bacteria like E. coli cannot be replaced by NusG proteins from the heat-resistant bacteria ”, says Johanna Drögemüller M.Sc., the first author of the article in Structure.

Another structural feature

The crystallographic analyzes in Berlin have shown that the protein NusG in the heat-resistant bacteria of the species Thermotoga maritima has another structural peculiarity: the amino-terminal domain itself contains a structural subunit. The functions of this structural element have not yet been clarified.

Source:

An Autoinhibited State in the Structure of Thermotoga maritima NusG
J. Drögemüller, et. al., Structure2013. DOI: 10.1016 / j.str.2012.12.015

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Heat protection protein of a particularly thermophilic bacterium clarified
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