Associate Professor Tony Roberton

Associate Professor

Microbiology

Phone: 09-3737599 x88233
Rm 106 or 103
Email: t.roberton@auckland.ac.nz

Mucin and Anaerobic Microbiology Laboratory

A layer of mucus covers the entire surface of the digestive tract. It forms a barrier protecting the delicate underlying cells from damage by digestive enzymes, acid, abrasion and bacteria. The major structural molecules of the mucus lyer are the mucins, which are huge glycoprotein molecules comprising a protein backbone covered in oligosaccharide (sugar) chains. In the colon especially, many of these mucin oligosaccharides chains are normally sulphated, and there is evidence that the rate of removal of this sulphate limits the breakdown of mucins by bacteria living in this region.

The Mucin and Anaerobic Microbiology group is studying both the structure and the properties of sulphomucins and the breakdown of sulphomucins by bacteria. The results will be important in understanding the processes by which mucus is normally protective, and what goes wrong in diseases where the mucus barrier functions abnormally.

For more information e-mail t.roberton@auckland.ac.nz or FAX us on +64 9 3737416

Research

We have discovered and purified a mucin desulphating sulphatase that removes sulphate from N-acetylglucosamine-6-sulphte groups of the mucin oligosassharide chains. The enzyme is produced by an anaerobic bacterium (Prevotella sp.) isolated from the colonic mucosa. The molecular biology and properties of this enzyme are being studied. The results will lead to studies on the changes in colonic sulphomucin in disease. For example, others have found that the activity of mucin-desulphating enzymes increases markedly in ulcerative colitis. we have found other sulphatases with different specificities in mucin degrading bacteria, and these are also being studied.

In a separate collaboration we are studying Helicobacter pylori, and investigating ways of preventing its growth in conditions similar to those in the stomach lumen and mucus layer.

Damian Wright

Mucins are the major structural component of the protective mucus barrier covering the gastrointestinal tract. Evidence is accumulating that desulphation of sulphated sugar residues attached to the oligosaccharide side chains of sulphomucin is the rate-limiting step for bacterial mucin degradation. This removal of sulphate from mucin occurs via sugar-specific sulphatases (1).

Previous work in this laboratory has focused on a N-acetylglucosamine-6-sulphate specific sulphatase involved in mucin degradation, from the anaerobic bacterium, Prevotella spp. An investigation of this enzyme at the molecular level has been undertaken and progress made.

In conjunction with this work, representative anaerobic bacteria from the gastrointestinal tract capable of degrading mucin glycoprotein have been screened. It is envisaged that enzymes exhibiting desired sulphatase activities and specificities from particular bacteria will be purified and characterised.

The availability of sulphatases with specificities for the sulphate groups in oligosacchahides and polysaccharides will potentially be useful in several fields of Glycobiology.

Publications

Roberton, A.M. and Wright, D.P. 'Bacterial glycosulphatases and sulphomucin degradation'. Can. J. Gastroenterol., 11, 361-366, 1997.

Douglas Rosendale

A brief overview of my PhD research topic is outlined below:

The internal epithelial surfaces of the gastrointestinal, respiratory and urogenital tracts are covered with a mucus gel. This continuous layer protects the underlying mucosa from pH extremes (stomach), digestive enzymes, toxins, chemicals, shear forces (peristalsis), and pathogenic and/or opportunistic invasion by bacteria and viruses. The main structural component of the mucus gel are the mucins, which are high molecular weight, heavily O-glycosylated glycoproteins. The removal of sulphate from the oligosaccharide component of sulpho-mucins has been proposed as a rate-limiting step in mucin degradation by bacterial enzymes. Bacteria possessing an enzyme capable of removing sulphate groups from mucin (a glyco-sulphatase) could pose a considerable threat to the integrity of the mucus barrier.

Previous work in this laboratory has identified certain bacterial strains prevalent in the colon of humans that possess sulphatases which are proposed to act primarily in the degradation of mucin. My main research goal, involving the disciplines of biochemistry and molecular biology, is to purify to homogeneity one of these sulphatases from a common species of colon anaerobe, and to establish the protein and DNA sequences.

My MSc research was also conducted in this laboratory. My project involved the disciplines of biochemistry and microbiology. I cultured selected Gram positive and Gram negative colon bacteria under anaerobic conditions and measured their to grow on trypsinised pig gastric mucin (PGMt, isolated and purified as part of the project). PGMt is sufficiently similar to human mucins, and those those strains of bacteria able to grow on it are likely to possess specialised mucin-degrading enzymes.

Cynthia Sun

Digestion of milk fat by pre-gastric lipase releases short chain fatty acids. These fatty acids could have significant suppressive effects on bacterial,viral or fungal food contaminants, particularly in the neonate stomachwhere acidity levels are low.

My research is to investigate some of the chemical and biochemical effects of the lingual lipase extracted from the tongues of calf and lamb. It is expected that the short chain fatty acids released will have important bactericidal effects in the stomach. Additionally the research will have important applications in animal neonate nutrition and disease prevention, and will highlight the potential effects of using infant milk formula.

Both chemical and microbiological approaches are needed in order to carry out my project. That is why I periodically appear in Thomas Building, although officially I am registered in Chemistry Department. My supervisor here - Associate Professor Tony Roberton and all the people in room 348 (especially Dr Sue Turner) have had to teach me basic microbiological techniques, answer my "never ending" questions, and put up with the horrible smells from the fatty acids which I work on. However, I am having a wonderful time working in SBS, no matter how many "troubles" I have brought with me.

Publications

• S F Mou, Q Sun and D P Lu. (1991) "Determination of xylose oligomers and monosaccharides by anion-exchange chromatography with pulsed amperometric detection". J. Chromatogr. 546, 289-295.
• Q Sun, S F Mou and D P Lu (1991) "Analysis of Monosaccharides in lipopolysaccharides by anion exchange chromatography with pulsed amperometric detection". Analysis Sciences, 7 (Suppl.), 157-160.
• Q Sun, H Wang and S F Mou (1995). "Rapid determination of germanium and tin by Ion Chromatography" J. Chromatogr. 708, 99-104.
• C J O'Connor, D T Lai and C Q Sun (1997). "Calf pregastric esterase catalyzed hydrolysis of 4-nitrophenylalkanoates: pH and temperature effects". J. Bioactive Compatible Polymers, 12, 140-154.
• C Q Sun, C J O'Connor, S J Turner, G D Lewis and A M Roberton (1997). "Theeffect of pH on the inhibition of bacterial growth by physiological concentrations of butyric acid: implications for neonates fed on suckled milk". Chem. Biol. Interactions (submitted).