Proline Repeats Aid Growth of Tooth Enamel, Study Shows

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Proline Repeats Aid Growth of Tooth Enamel, Study Shows
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News Release

 

[Writer] This is research news from U-I-C – the University of Illinois at Chicago.

Today Tom Diekwisch (Deek-Wish), professor and head of the department of oral biology at the College of Dentistry, talks about how a simple amino acid that is repeated in the center of proteins found in tooth enamel makes teeth stronger and more resilient.

Here’s Professor Diekwisch:

[Diekwisch] One of our interests in our research has been about teeth in various animals. What distinguishes a frog from a mouse? Do frogs have teeth? Have you ever checked a frog’s mouth and seen the teeth in a frog’s mouth? Frogs do have teeth in their upper jaws and, in fact, they also have enamel on the teeth. Is the enamel like human enamel, or is it different?

What we did was sequence the key enamel protein in frogs and in mice, and compared them. The one in the mice had much longer polyproline repeat stretches than the one in the frogs. And that caught our attention.

We thought perhaps from a developmental perspective, the length of the polyproline repeat was important for the way enamel grows in frogs or in mice. In order to test our thinking, we then made artificial proteins – polypeptides – with proline repeats of various lengths and subjected them to enamel crystal growth conditions.

The longer the polyproline stretches were, the longer the enamel crystals were, when we grew them under artificial conditions.

Then we realized that we had discovered a new principle of how to affect the growth of enamel crystals, perhaps also for in vitro conditions. If we ever were to grow new enamel, we would know we would have to have these long polyproline repeat peptides in there somewhere.

But when we were trying to understand how does it happen that these long sequence stretches also make the crystals grow long, that’s actually where our research became exciting.

When we made peptides from these long repeats, those supra-molecular aggregates – those “bubbles” – that these peptides form in fact were, counter-intuitively and surprisingly, smaller with the longer stretches and bigger with the shorter stretches.

The interesting thing was, the longer the polyproline repeat stretches were, the smaller the bubbles became. And that was counter-intuitive.

So we asked the question, biochemically, how might that happen?

So we looked at the structure of these longer stretches – and, in fact, also did a 3-NMR structure of these proteins – and we found the longer the stretches are, the more unique structural fold elements – polyproline type-2 helices – are in these sequences that help to fold-up those aggregates. So even though the stretches are longer – because there are more polyproline type-2 helices – the proteins become more folded and form smaller bubbles.

So polyproline repeats not only exist in enamel proteins, they exist in many proteins. They exist in anti-freeze proteins, they exist in mucins, they exist in the proteins of neurodegenerative diseases.

So we have, for the first time, discovered the principles of how these polyproline repeat stretches have a functional impact on the real-worldliness of proteins in a physical being. They make them more compact. And the more compact these physical aggregates are, the more they can affect the growth of entities within nature. That is in fact a totally new understanding of the role of these very universal principles.

We hope that from this discovery, we not only know how to make enamel, or perhaps have a beginning toward that story, but we also hope that this insight will help us perhaps with a cure for neurodegenerative diseases. Or, help us make cooler antifreeze proteins, or other designer proteins, that will significantly advance biotechnology.

[Writer] Tom Diekwisch is a professor and head of the department of oral biology in the College of Dentistry.

For more information about this research, go to www.news.uic.edu … click on “news releases.” … and look for the release dated December 21, 2009.

This has been research news from U-I-C – the University of Illinois at Chicago.

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