Figure 1 . (a) The lipoylation process of H protein in E. coli and the shuttling role of lipoylated H protein in the glycine cleavage system. LplA catalyzes the lipoylation process in two steps: 1. Adenylation of lipoic acid, and 2. lipoate transfer to H protein(Morris et al. 1995). (b) Main conformational changes of LplA during the lipoylation process. LplA contains a N-terminal domain and a movable C-terminal domain. The latter rotates from a bending (closed) conformation to a stretched (open) conformation upon binding of lipoate and ATP and probably under the effect of Hapo (Fujiwara et al. 1991). Key secondary structures of the C-terminus are indicated by colors: β-12 in yellow, β-13 in orange, β-14 in red, α-8 in magenta, α-9 in blue, α-10 in beige.