[1] Univ British Columbia, Dept Biochem, Vancouver, BC V6T 1Z3, Canada
[2] Univ British Columbia, Dept Microbiol, Vancouver, BC V6T 1Z3, Canada
[3] Univ Laval, Dept Med, Ste Foy, PQ G1K 7P4, Canada
[4] Univ Laval, Dept Chem, Ste Foy, PQ G1K 7P4, Canada