Understanding the biological functions of proteins, especially those of enzymes, is greatly facilitated by the knowledge of their three-dimensional structures. Our laboratory has a long-standing interest in the hydrolytic mechanisms of the serine and aspartic proteinases and their inhibitors (Maynes et al. , 2005; Barrette-Ng et al. , 2003a,b; Ng et al. , 2000), the glycosyl hydrolases and their transition state mimics lysosomal b -hexosaminidase B (Mark et al. , 2003). From these studies we have amassed a wealth of structural information for the interpretation of ligand binding specificity, and the chemical pathways for the hydrolysis of good substrates.

One of the major projects in the laboratory is the structural genomics of Mycobacterium tuberculosis . In this project our laboratory has targetted 160 ORFs from the Mtb genome; we have expressed ~ 120 of these proteins on a small scale and have expressed ~ 40 on a mg scale for purification and crystallization. We have crystallized 12-13 of the purified proteins and have solved the structures of 6 (for example, Maynes et al. , 2003). All of the 160 targetted ORFs did not have a known function at the time of targeting and our structural studies have contributed to the determination of their functions in the tubercular bacillus.

Our laboratory has contributed much to the elucidation of the role of virally encoded enzymes in the maturation and infectivity of RNA viruses, such as: poliovirus, hepatitis A virus, rhinovirus 2, rabbit hemorrhagic disease virus and hepatitis C virus. We have shown that the fold of the 3C proteinases resembles that of the chymotrypsin family of serine proteinases but the nucleophile is the sulfur atom of a cysteine residue (Bergmann et al. , 1999; Bergmann et al. , 2000). The 2A proteinase from Rhinovirus 2 also has a chymotrypsin-like fold and an active site cysteine but it is much smaller (140 residues) than the 3C enzymes from enteroviridae and Rhinoviridae (Petersen et al. , 1999). Other targets for anti-viral compounds are the RNA dependent RNA polymerases. We have determined the structures of the RdRp from rabbit hemorrhagic disease virus (Ng et al. , 2002) and from hepatitis C virus (HCV). Working in collaboration with ViroChem Pharma Inc. we have determined the structures of inhibitors bound to HCV NS5B. These inhibitors bind to an allosteric site ~ 35 Å from the polymerase catalytic site (Wang et al. , 2003; Biswal et al. , 2005).

Glycosyl hydrolases are directly linked to lysosomal storage diseases. Genetic defects in the b subunit of b hexosaminidase B are associated with Sandhoff disease whereas genetic defects in the a -subunit of Hex A are associated with Tay-Sachs disease. We have determined the structure of Hex B ( the homodimer of b -subunits (Mark et al. , 2003) ) and are currently working on the structure of Hex A (the heterodimer of a and b -subunits). We are collaborating with Don Mahuran of the Hospital for Sick Children on this research. Don and his group have shown that chemical chaperones (small molecule inhibitors) will enhance the enzymatic activity of HexA and HexB in the lysosomes so part of our research is directed at identifying the binding sites of these molecules.

Our group is part of an NSERC and PENCE funded team that is working on the structures of inhibitors bound to the SARS proteinase. We have determined the structure of the SARS proteinase in three new space groups. These structures have been used to describe several new inhibitors that bind tightly to the enzyme that functions as a dimer. These inhibitors are based on a new warhead for cysteine proteinases along with a tripeptide address moiety with a P1 glutamine. This work defines the binding sites S4, S2 and S1 very clearly and is helping us to design new inhibitors of the SARS proteinase.

Protein phosphatase-1 (PP-1) and protein phosphatase 2B (calcineurin) are eukaryotic serine/threonine phosphatases that share ~ 40% amino acid sequence identity in their catalytic subunits. We have determined the structures of PP-1 bound to okadaic acid (Maynes et al. , 2001) and other natural product marine toxins (Holmes et al. , 2002). We have also explored the structural consequences of mutations in the b 12- b 13 loop region on the binding of okadaic acid, microcystin LR and protein phosphatase inhibitor 2 (Maynes et al. , 2004). This information will assist in the design of inhibitors of calcineurin, the protein phosphatase implicated in immunosuppression for organ transplantation.

Our laboratory has determined the 3D structure of Scytalidoglutamic proteinase (SGP), a completely new family of proteolytic enzyme, G1 (Fujinaga, 2004). We have shown that this family adopts a unique tertiary structure that is a new proteolytic enzyme fold. As well SGP has a unique hydrolytic mechanism for catalysis that depends on a glutamic acid carboxylate, a glutamine carboxamide and a nucleophilic water molecule. We have named this proteolytic family the EQOLISINS . From the structural work we have designed a nanomolar inhibitor of SGP and are working on the structure of the inhibitor bound to SGP.