Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore. lawrence@bic.nus.edu.sg|Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore. lawrence@bic.nus.edu.sg|Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore. lawrence@bic.nus.edu.sg