New method allows scientists to watch an enzyme at work

Image credit: AJC1 via Flickr

A team at the University of Bonn, Germany, have developed a new method of ‘photographing’ enzymes at work in order to study the behaviour of the enzyme as it works.

Enzymes are protein structures which help reactions to take place, they are often referred to as ‘chemical catalysts’ and they perform a wide array of functions throughout biology. Enzymes are specific to one reaction, so each reaction has an enzyme which is suited to the substrates involved. Substrates are molecules or compounds which enzymes work on to carry out a reaction of some kind, for example this might be to hold two substrates in a particular orientation so that they can react. In order to encourage a reaction, an enzyme must be more than a stationary protein, the process of catalysing a reaction usually involves some conformational changes in an enzyme, though when the reaction is complete the enzyme returns to its original state ready to start over with fresh substrates.

Methods of characterising enzymes are already highly advanced, scientists can determine the structure of an enzyme, but a still image is not very useful when investigating something which has motion. Prof. Dr. Olav Schiemann from the Institute of Physical and Theoretical Chemistry at the University of Bonn explained that as the movements of  enzymes cannot be seen, understanding how they work is very difficult. This new method can show scientists how an enzyme behaves while it is in action.

Pulsed EPD dipolar Spectroscopy (PDS) is the existing method for investigating enzyme behaviour, it measures the distance between metal centres of enzymes, but this method is unsuitable for an important group of enzymes which have metal ions with numerous unpaired electrons, called ‘high-spin ions’ in their catalytic centres. This group includes haemoglobin, an enzyme found in red blood cells which uses an iron ion at its catalytic centre to bind oxygen for transportation in the blood. With this method unsuitable for this use, the team set out to develop a suitable one.

Dr Dinar Abdullin explained that the team developed a new method which uses the high-spin ions to their advantage, because they act like electromagnets and can randomly change their polarity, meaning that their north and south poles can switch at random, which is called ‘flipping’. This is used to measure distances between different parts of the enzyme by linking the enzyme with other chemical compounds which also have electromagnetic properties. This is done so that when the metal ion ‘flips’, the compound attached also changes its polarity. The nature of how the attached compound does this is dependent on multiple things, one of which is the distance between it and the high-spin ion in the catalytic centre, which allows the scientists to determine the distance.

By using several magnetic groups bound to one enzyme, it is possible to determine the distance between each of the groups and the catalytic centre, which can allow scientists to watch how the position of the catalytic centre changes in relation to the other magnetic groups during catalysis.

This sounds very advanced, and it is, but the team don’t actually watch the enzyme work. The measurements are taken from enzymes frozen at different timepoints and therefore different stages of catalysis, then the measurements are determined from each timepoint and strung together. This is more like watching a stop-motion video, made from a series of still images one after the other, than a film.

The team hope to further their work and eventually use it to investigate the development of certain diseases that are triggered by functional disorders of enzymes.

This post was written by Molly Eastol and edited by Ella Mercer.

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