[1] Univ Cambridge, Yusuf Hamied Dept Chem, Cambridge CB2 1EW, England
[2] Transit Bio Ltd, Cambridge, England
[3] Natl Inst Diabet & Digest & Kidney Dis, Lab Chem Phys, Natl Inst Hlth, Bethesda, MD 20892 USA
[4] Univ Cambridge, Dept Genet, Cambridge CB2 3EH, England
[5] Univ Cambridge, Dept Phys, Cavendish Lab, Cambridge CB3 0HE, England