A recombinant levansucrase from Bacillus licheniformis 8-37-0-1 catalyzes versatile transfructosylation reactions

• Purification, gene cloning and expression of Bacillus licheniformis levansucrase (SacB).
• The SacB synthesized maximal yield of levan with molecule mass of 9.6 × 106 from 0.8 M sucrose (pH 6.5) at 40 °C for 24 h.
• The SacB transferred fructosyl to various saccharides and branched alcohols.
• Chemical structures of the transglycosylation products were analyzed by MS and NMR.

This work disclosed the broad transglycosylation capability of the levansucrase from Bacillus licheniformis 8-37-0-1 for the first time. The levansucrase was firstly purified from the strain 8-37-0-1 and found to be a monomer of ∼51 kDa with KETQDYKKSY as the N-terminus. Then, the gene encoding the enzyme was cloned and it contained an ORF of 1449 nucleotides, encoding a 482 amino-acid protein with a predicted 29 amino-acid signal peptide. The deduced mature protein without the signal showed the same N-terminus to the purified enzyme. The mature enzyme was subsequently expressed in Escherichia coli. The recombinant enzyme showed similar biochemical properties to the native one. It produced maximal yield of 7.1 mg/mL levan (Mr 9.6 × 106) from 0.8 M sucrose (pH 6.5) at 40 °C for 24 h in vitro. When using sucrose as the donor, the enzyme displayed a wide range of acceptor specificity and was able to transfer fructosyl to a series of sugar acceptors including hexose, pentose, β- or α-disaccharides, along with the difficult branched alcohols that have not been investigated before. Chemical structures of the resultant products were analyzed by MS and NMR spectra.