Our research mainly centres on elucidating various aspects of the structure-function relationship of metalloproteins. In this regard, we are currently focusing on a variety of zinc enzymes, including anthrax lethal factor (LF), metallo-β-lactamases, thermolysin and carboxypeptidase A. We are also interested in the development of bioanalytical techniques.
Anthrax Lethal Factor
Anthrax is an infectious disease caused by the rod-shaped, Gram-positive bacterium Bacillus anthracis. The disease mainly affects animals (mainly cattle and other herbivores), but can occasionally be transferred to humans. The toxic effects associated with anthrax are mainly a consequence of the secretion of three proteins which constitute the anthrax toxin. These are: the protective antigen (PA), the lethal factor (LF), and the edema factor (EF). The protective antigen, so-called for its use in vaccines, is responsible for the translocation of LF and EF into the host cell cytosol where these proteins function enzymatically.
LF is a zinc-dependent metallo-endopeptidase (90 kDa) that catalyzes the cleavage of mitogen-activated protein kinase kinases (MAPKKs). Proteolysis of MAPKKs leads to a disruption of major cell signaling pathways (with potentially deadly consequences). The active site of LF is comprised of a single Zn(II) ion, which is tetrahedrally coordinated to three amino acid residues (His686, His690, Glu735) and a single water molecule. The Zn(II) ion activates the water molecule for attack on the MAPKK substrate.
Our research relating to LF centers on elucidating the metal requirement and mechanism of the enzyme. For instance, we have found that incorporating cobalt and especially copper instead of zinc can “hyperactivate” LF. In addition, we are studying the more general mechanisms by which metal ions exchange in metalloproteins, using LF as a prototype. Finally, we are interested also in the folding/unfolding of LF, and in the fate of the zinc ion during these processes since the enzyme needs to be first unfolded to reach the interior of host cells, and then requires to be refolded in order to be active.
Metallo-β-lactamases
β-Lactamases are enzymes which are capable of inactivating β-lactam antibiotics by amide bond hydrolysis. These enzymes are the major contributors to the emergence of microbial resistance to β-lactam antibiotics such as penicillins. There are four distinct classes of β-lactamases (designated A to D). Class B enzymes (termed metallo-β-lactamases, MBLs) are zinc-dependent, and require one or two zinc ions for their function. In recent years, MBLs have received considerable attention since they hydrolyze most β-lactams, including penicillins, cephalosporins, clavulanic acid, penicillanic acid sulfones and carbapenems.
Our research on MBLs focuses on the inhibition of these enzymes. In collaboration with Dr. Gary Dmitrienko (University of Waterloo, ON), we are involved in investigating a variety of small molecules (some of them bearing zinc-binding groups) to find potent inhibitors of these enzymes that could be further developed into drug candidates. In addition, we are interested in gaining some insight into the molecular details and mechanisms of MBL-inhibitor interactions.
Development of bioanalytical techniques
We are interested in developing simple and cost-effective analytical techniques for the determination of metal ions in biological samples (in particular metalloproteins) using simple chromophoric and fluorescent compounds. We are also involved in developing sensitive enzyme assays for zinc enzymes as well as (more recently) for the main protease (Mpro) of SARS-CoV2 (the virus that causes COVID-19). Finally, we are currently exploring the possibility of using chromophoric (coloured) zinc-binding compounds to study structural changes in zinc enzymes that occur when these proteins are forced to unfold.