A bug’s death Targeting iron uptake in pathogenic bacteria A group in Edinburgh is exploring iron uptake in pathogenic bacteria. Could this be their Achilles heel?

Iron is essential to survival but often in short supply. As a result, organisms have evolved sophisticated ways of extracting it from the environment. At the University of Edinburgh, Dominic Campopiano and Professor Peter Sadler have been awarded a Showcase grant to study a particularly interesting iron-uptake system so far found only in pathogenic bacteria. It is thus an excellent therapeutic target, as treatments would interfere with an essential biochemical pathway but would affect only harmful bacteria.

The iron-uptake system is a form of molecular mugging. The bacteria seize hold of transferrin – a large protein that transports iron around the body – and relieve it of its precious cargo. Key to this snatch-and-grab operation is the Fe-binding protein (FBP), which appears to shuttle iron between the inner and outer membranes of the bacteria.

Dr Campopiano and Professor Sadler work in the Department of Chemistry at Edinburgh, which has a long tradition of biologically oriented research. Moreover, while calling upon a selection of expertise within chemistry, they also turn to an extensive network of contacts for more biological and clinical work. The FBP work is a relatively recent departure. "About a year and a half ago I didn’t know anything about FBPs," says Dr Campopiano. "Peter Sadler walked into the lab with some DNA in an Eppendorf tube and said, ‘A Canadian professor’s sent me some DNA from a pathogenic bacterium: what do I do with it?’" The DNA turned out to code for an FBP from Neisseria gonorrhoeae, and various members of the lab set about making the FBP protein and exploring its properties. "The grant is actually built on preliminary work done by fourth-year undergraduate students and a PhD student of Peter Sadler’s," says Dr Campopiano. The Showcase grant provided a perfect opportunity to take this preliminary work forward.

Work is being focused on Actinobacillus actinomycetemcomitans (AA), which as well as being a mouthful to say, is also a major cause of tooth decay. Although antibiotics kill AA, they are not discriminating. "There are hundreds of different species of bacteria in your mouth," points out Dr Campopiano, "and you need them for a healthy mouth." A specific antibiotic against AA would thus be highly desirable, and its FBP – not shared with its harmless mouth-dwelling relatives – would be an ideal target.

Furthermore, the preliminary work identified another exciting lead. Professor Sadler’s group has also been developing a range of anticancer compounds. To their surprise, they found that these compounds not only bound to FBP, but actually displaced iron from its binding site. Since the anticancer compounds have few side-effects, they offer the exciting possibility of AA-specific antibiotics.

Getting hold of the AA protein turned out to be unexpectedly problematic. The FBP gene had been recently cloned by a European group, but they had moved on and were reluctant to get involved. "I knew it was in a freezer somewhere in Holland, but I couldn’t get at it," says Dr Campopiano. Undaunted, he went back to the DNA and protein databases and discovered that a group in Japan led by Susumu Kokeguchi had also cloned the gene. Dr Kokeguchi was delighted to be involved. The DNA duly arrived, and the Edinburgh and Japanese groups have collaborated ever since.

Dr Campopiano will be exploring the structure of FBP in more detail, comparing the FBPs turning up in other bacteria, and characterising the binding of their metal compounds. All this can be carried out in-house, while Professor Denis Kinane in Glasgow – who has also previously worked with Dr Kokeguchi – will be providing clinical isolates of AA and helping the group test the antibiotic activity of the new compounds.

The group will also be using mass spectrometry, proteomic analysis and DNA microarrays (via a collaboration with Douglas Roy in the Edinburgh Genomic Microarray Facility) to gather information on a genomic scale about AA. "You can watch what’s actually happening as the bacteria are hit with iron, or antibiotics, or even blood extracts," says Dr Campopiano. This work may or may not confirm the potential of FBP: "If you starve the cell of iron, then add it back, it would be great to see the first protein that turned on is FBP because that means we’ve got the best target. But if it turns on three or four genes, that’s great – they’re potential other targets as well."

See also

• Showcase awards: Funding details
• Brainy Babies: Article describing (Showcase funded research) on prenatal stimulation
• Gas Attack: Article describing (Showcase funded research) research to develop a device to safeguard divers
• Thinking Big: Article describing (Showcase funded research) on the development of biodegradable polymers for use in drug delivery

External links

• University of Edinburgh: Research interests of Peter Sadler
• Department of Chemistry: Departmental research interests at the University of Edinburgh

Further reading

Dr Dominic Campopiano
Leadbeater C, McIver L, Campopiano D J, Webster S P, Baxter R L, Kelly S M, Price N C, Lysek D A, Noble M A, Chapman S K, Munro A W (2000). Probing the NADPH binding site of Escherichia coli flavodoxin oxidoreductase Biochem. J., 352: 257-266.

McIver L, Baxter R L, Campopiano D J (2000). Identification of the [Fe–-S] cluster-binding residues of Escherichia coli biotin synthase. Journal of Biological Chemistry 275(18): 13888–13894.

Webster S P, Alexeev D, Campopiano D J, Alexeeva M, Watt R M, Sawyer L and Baxter R L (2000). Biochemistry 39(3): 516–528.

Ellis J, Campopiano D J, Izard T (1999). Acta Cryst. D55: 1086–1088.

Alexeev D, Alexeeva M, Baxter R L, Campopiano D J, Webster S P, Sawyer L (1998). Journal of Molecular Biology 284: 401–419.

McIver L, Leadbeater C, Campopiano D J, Baxter R L, Daff S N, Chapman S K, Munro A W (1998). European Journal of Biochemistry 257: 577–585.

Alexeev D, Baxter R L, Campopiano D J, McAlpine R S, McIver L, Sawyer L (1998). Tetrahedron 54: 15891–15898.

Mosher R H, Campopiano D J, Brown M P, Yang K, Shaw W V, Vining L C (1995). Journal of Biological Chemistry 270(45): 27000–27006.

Baxter R L, Campopiano D J, Coutts A, Shaw N (1992). J. Chem. Soc. Perkin Trans. 1: 255–258.

Professor Peter J Sadler
Sun H, Li H, Mason A B, Woodworth R C, Sadler P J (1999). N-Lobe versus C-lobe complexation of bismuth by human transferrin. Biochem. J. 337: 105–111.

Sun H, Li H, Sadler P J (1999). Transferrin as a metal ion mediator. Chem. Rev. 99: 2817–2842.

Cox M C, Barnham K J, Frenkiel T A, Hoeschele J D, Mason A B, He Q-Y, Woodworth R C, Sadler P J (1999). Identification of platination sites on human serum transferrin using 13C and 15N NMR spectroscopy. J. Biol. Inorg. Chem., 4: 621–631.

Guo M, Sun H, Bihari S, Parkinson J A, Gould R O, Parsons S, Sadler P J (2000). Stereoselective formation of seven-coordinate titanium(IV) monomer and dimer complexes of ethylenebis(o-hydroxyphenyl)glycine. Inorg. Chem. 39: 206–215.

Guo M, Sun H, McArdle H J, Gambling L, Sadler P J (2000). Ti(IV) uptake and release by human serum transferrin and recognition of Ti(IV)-transferrin by cancer cells: understanding the mechanism of action of the anticancer drug titanocene dichloride. Biochemistry, 39: 10023–10033.

Guo M, Sadler P J (2000). Competitive binding of the anticancer drug titanocene dichloride to N,N´-ethylene(o-hydroxyglycine) and adenosine triphosphate: a model for Ti(IV) uptake and release by transferrin. J. Chem. Soc. Dalton, 7–9.

Guo Z, Sadler P J (1999). Metals in Medicine. Angew. Chem. 111: 1610–1630; Angew. Chem. Int. Ed., 38: 1512–1531.

Guo Z, Sadler P J (1999). Medicinal inorganic chemistry. Adv. Inorg. Chem. 49: 183–306.

Kratochwil N A, Parkinson J A, Bednarski P J, Sadler P J (1999). Nucleotide platination induced by visible light. Angew. Chem. 111: 1566–1569; Angew. Chem. Int. Ed. 38: 1460–1463.

Chen Y, Parkinson J A, Guo Z, Brown T, Sadler P J (1999). A new platinum anticancer drug forms highly stereoselective adduct with duplex DNA. Angew. Chem. 111: 2192–2196; Angew. Chem. Int. Ed. 38: 2060–2063.

Murdoch P del S, Kratochwil N A, Parkinson J A, Patriarca M, Sadler P J (1999). A novel dinuclear diaminoplatinum(II) glutathione macrochelate. Angew. Chem. 111: 3062–3065; Angew. Chem. Int. Ed. 38: 2949–2951.

Kratochwil N A, Ivanov A I, Patriarca M, Parkinson J A, Gouldsworthy A, Murdoch P del S, Sadler P J (1999). Surprising reactions of iodo Pt(IV) and Pt(II) complexes with human albumin: detection of Cys34 sulfenic acid. J. Am. Chem. Soc. 121: 8193–8203.

Sun H, Li H, Harvey I, Sadler P J (1999). Interactions of bismuth complexes with metallothionein(II). J. Biol. Chem. 274: 29094–29101.

Zou J, Taylor P, Dornan J, Robinson S P, Walkinshaw M D, Sadler P J (2000). First X-ray crystal structure of a medicinally-relevant gold protein complex: unexpected binding of Au(PEt3)+ to histidine. Angew. Chem. 112: 3054–3057; Angew. Chem. Int. Ed. 39: 2931–2934.

Parkinson J A, Chen Y, Murdoch P del S, Guo Z, Berners-Price S J, Brown T A, Sadler P J (2000). Sequence-dependent bending of DNA induced by cisplatin: NMR structures of an AT rich duplex. Chem. Eur. J. 6: 3636–3644.