Interestingly, the stability of AtGUS(-3t)-E was slightly higher than that of AtGUS-E at 65uC. Similar results have been reported that the modification of the C-terminal region could improve the thermal stability of endo-b-glucanase from Bacillus subtilis JA18 [11] . In addition, previous study showed that ab-loops in ''stability face'' are important for the stability [22] . The truncation of the non-conservative sequence lies near ab-loops of the stability face, therefore, we can predicted that the deletion of the C-terminal region outside the TIM barrel domain has influence on thermal stability of AtGUS. The effect of nine metal ions with different concentration gradients on the activities of AtGUS(-3t)-E and AtGUS-E was evaluated, and Co 2+ , Ca 2+ , and Ni 2+ showed opposite effects on the two enzymes, respectively. In addition, AtGUS(-3t)-E showed higher affinity and catalytic efficiency than AtGUS(-3t)-E. Both of the result might suggest that the spatial structural rearrangement, and the speculation has been proved by CD spectra, which showed great difference between the secondary structure of the two enzymes. It has been reported that the loops above the catalytic face was very important for substrate hydrolysis [23] , so we can conclude that the truncation of the non-conservative domain firstly changed the secondary structure of the enzyme and then influenced the substrate affinity, catalytic efficiency and metal ions effects. Moreover, the crystal structure of human bglucuronidase was firstly reported in 1996 [24] , and the structure of bacterial b-glucuronidase has also been published recently [25] . Both b-glucuronidase structures were tetramers. The deleted region of the AtGUS non-conservative sequence lies outside the main three domains, so it was predicted that the non-conservative might change the combination pattern of each monomer.