The TIM barrel domain is a canonical (b/a) 8 -barrel composed of eight units, each of which consists of a b-strand and an a-helix [20] . There was a non-conservative segment behind the catalytic domain (TIM barrel domain) of AtGUS which showed low identity with PGUS and AuGUS after the primary sequence alignment. A model of the three-dimensional structure of AtGUS was presented in the current research ( Figure 7) . The deleted sequence exhibited no involvement in the TIM barrel domain, locating near the ''stability face'' rather than the ''catalytic face'' [21] .