Swammerdam Institute for Life Sciences

Focus on research: molecular biologist Frans Klis

Frans Klis offers an apology as he opens a PowerPoint presentation to illustrate his research with a few pictures. ‘We'll skip the worst of these, he says, clicking past photographs of a white tongue, a red baby bottom and severely infected fingernails. All fungal infections, and mainly caused by Candida albicans, the subject of Klis' research. He isn't all that interested in the clinical pictures: Klis' focus is on the protein coats contained in these fungi. He is trying to identify a protein component that other researchers can use in developing a vaccine against the fungus.

As a biologist, Klis began his career studying cell wall enzymes in plants. He subsequently shifted his focus to algae and then to yeast. From here, it was a small step to other fungi, such as Candida, one of his current areas of focus. The fungus offers one major advantage: ‘There's a medical side to the Candida story. That makes it easier to get funding for my research.' Interestingly enough, the fungus is extremely similar to normal baker's yeast. Klis: ‘They're almost impossible to distinguish in morphological terms.'

Frans Kils

Photo: Bob Bronshoff

Yeast and hyphal forms

However, their modes of existence do differ. As Klis explains, Candida is entirely adjusted to living in and on warm-blooded animals, including humans. Amongst other conditions, the fungus causes skin infection, but also feels right at home on the mucosae in the vagina and mouth. Another important difference: Candida occurs in the common ‘yeast' form - single cell globes with a diameter of several micrometres - as well as hyphal form, in which the fungus forms long strands.

To illustrate his point, Klis shows photographs of an experiment with fungal colonies in Petri dishes. ‘An animal mucosal protein was added to the agar in the Petri dishes: this allows us to simulate mucosae', he explains. One Petri dish has a neutral pH value of 7, comparable to the acidity level in the mouth, while the other has a pH of 4, similar to the environment inside the vagina. The fungal colonies certainly appear to be thriving in both dishes.

Having rinsed off the dishes with water, Klis now shows us an entirely different picture. The acidic agar dish is clean, while the fungal colony on the pH-neutral dish has managed to cling on. This demonstrates the difference between a colony consisting of yeast-form cells and a colony that attaches itself to its environment with hyphae. As Klis explains, this very same process can take place in the human body.

Klis' research employs a range of other tricks to induce hyphal growth, such as raising the temperature to 37 degrees or increasing the CO2 content to 5 percent. ‘We're basically recreating the conditions in the human body.'

Surface proteins

Candida has a number of other special tricks up its sleeve that allow it to survive in unnatural environments. The tongue, for example, where Candida can attach itself firmly to the epithelial cells, Klis explains. These cells keep out intruders by intermeshing proteins on their surface, so that they cannot be penetrated by unwanted guests such as bacteria. However, Candida has its very own surface protein that closely resembles the substrate of this intermeshing system. The epithelial cells will form bonds with Candida rather than one another, after which the fungus can no longer be removed.

As Klis explains, the fungus has dozens of these surface proteins, which form the main focus of his research. Under a microscope, they appear to form a hairy cloak, attached to the cell wall. The proteins play a crucial role in interactions with the host, and are responsible for adhesion. Other proteins play a part in the defence against the body's chemical attacks. Klis shows a picture of a white blood cell absorbing yeast-form fungi. The next photo shows the fungus cells after having progressed to hyphal growth mode with hyphae extending from all sides of the blood cell.

A vaccine against fungi

The exact composition and quantity of proteins in the protein coat depend on the fungus type - yeast or hyphal - and the circumstances under which it develops. Klis and his group have now identified and characterised all twenty to thirty proteins in the Candida coat, and painstakingly charted the peptides of which they consist.

They hope their efforts will help in combating the fungus. As Klis explains, there are currently a number of medications on the market, such as the familiar tube of anti skin infection cream. However, these azoles, as they are known, are not always equally effective, and do not help control all forms of Candida. This is why scientists have been searching for a vaccine against the fungus for the past ten years. Such a vaccine would help the body recognise the fungus and take appropriate measures. This recognition system, Klis explains, will have to be targeted at the surface proteins.

As he explains, another research group spent years working on a peptide taken from a Candida surface protein. They even managed to develop a specific vaccine. ‘They then infected vaccinated mice with Candida. Unfortunately, the mice still died of the infection. As it turned out, the vaccine was only effective against the yeast form, and simply didn't recognise the hyphal form.'

The ideal vaccine, in other words, will have to be based on a peptide occurring in both the yeast and hyphal surface proteins. Unfortunately, the protein makeup of these two types tends to differ significantly. Klis is hoping to find a single peptide that occurs in all fungal types, or a combination of peptides from various proteins. ‘Last year, we published the entire genome sequences for the infectious Candida species in collaboration with an international consortium. We examined the cell walls and identified three families of cell wall proteins that are genuinely unique to infectious strains of Candida. They do not occur in other types of Candida or yeast. We suspect that these proteins are also involved in the infection process; they may well be suitable for use in a vaccine.'

Klis applied bioinformatical algorithms to select a number of candidate peptides for a new vaccine. He is currently testing them under various conditions. His research group is working as part of an international collaborative that includes an Aberdeen-based company capable of developing a marketable vaccine on the basis of a suitable peptide. So, will we have a vaccine within ten years? ‘I can't say for sure, but the chances are certainly looking good.'

See also

Published by  Faculty of Science

21 August 2012