Using signal peptide prediction with caution, a case study in Aspergillus niger xylanase

摘要

Signal peptide (SP) prediction is used, but not known correct or not. The Aspergillus niger GH10 xylanase (XynB) SP is predicted to be 1-19 (Met_1-Ser_(19)) residue, differing from the Penicillium simplicissimum xylanase 1-25 residue SP. To determine the real SP, two types of XynB, Xyn△19 and Xyn△25, were constructed by respectively deleting the 19 (Met_1-Ser_(19)) or 25 (Met_1-Arg_(25)) residues. The Xyn△25 had 10℃ higher T_(opt), and 21.6-times longer thermostability than the Xyn△19 (46 vs. 36 ℃ and 47.6 vs. 2.2 m). When the kinetics were assayed, the Xyn △25 had ～2.1 -times higher V_(max) and higher binding-affinity for xylan than the Xyn△19 (53.7 vs. 25.3 μmol/ml/m and 2.43 vs. 2.96mg/ml). Thus, the XynB real SP is the 1 -25 and not predicted 1-19 residues. The extra six N-terminal residues (Glu_(20)Pro_(21) He_(22)Glu_(23) Pro_(24)Arg_(25)) drastically interfered with the Xyn△19 thermal activity, thermostability, and catalytic efficiency.