N-Terminal Domain Truncation and Domain Insertion-Based Engineering of a Novel Thermostable Type I Pullulanase from Geobacillus thermocatenulatus

摘要

A novel thermostable type I pullulanase gene (pul(GT)) from Geobacillus thermocatenulatus DSMZ730 was cloned. It has an open reading frame of 2154 bp encoding 718 amino acids. G. thermocatenulatus pullulanase (Pul(GT)) was found to be optimally active at pH 6.5 and 70 degrees C. It exhibited stable activity in the pH range of 5.5-7.0. Pul(GT) lacked three domains (CBM41 domain, X25 domain, and X45 domain) compared with the pullulanase from Bacillus acidopullulyticus (2WAN). Different N-terminally domain truncated (730T) or spliced (730T-U1 and 730T-U2) mutants were constructed. Truncating the N-terminal 85 amino acids decreased the K-m value and did not change its optimum pH, an advantageous biochemical property in some applications. Compared with 2WAN, Pul(GT) can be used directly for maize starch saccharification without adjusting the pH, which reduces cost and improves efficiency.