1. Department of Chemistry Simon Fraser University Burnaby BC V5A 1S6 Canada
2. Department of Chemistry Graduate School of Science The University of Tokyo 7-3-1 Bunkyo-ku Tokyo 113-0033 Japan
3. York Structural Biology Laboratory Department of Chemistry University of York York YO10 5DD UK
4. Department of Molecular Biology and Biochemistry Simon Fraser University Burnaby BC V5A 1S6 Canada