Biochemical characterization of two new Aspergillus niger aspartic proteases

Peng Song; Lei Cheng; Kangming Tian; Meng Zhang; Nokuthula Peace Mchunu; Dandan Niu; Suren Singh; Bernard Prior; Zheng-Xiang Wang

doi:10.1007/s13205-020-02292-4

Biochemical characterization of two new Aspergillus niger aspartic proteases

3 Biotech. 2020 Jul;10(7):303. doi: 10.1007/s13205-020-02292-4. Epub 2020 Jun 13.

Authors

Peng Song^{1

2}, Lei Cheng^{1

2}, Kangming Tian², Meng Zhang², Nokuthula Peace Mchunu³, Dandan Niu², Suren Singh⁴, Bernard Prior⁵, Zheng-Xiang Wang²

Affiliations

¹ College of Biotechnology, Tianjin University of Science and Technology, Tianjin, 300457 China.
² Department of Biological Chemical Engineering, College of Chemical Engineering and Materials Science, Tianjin University of Science and Technology, Tianjin, 300457 China.
³ Agricultural Research Council, Biotechnology Platform, Private Bag X5, Onderstepoort, 0110 South Africa.
⁴ Department of Biotechnology and Food Technology, Faculty of Applied Sciences, Durban University of Technology, P. O. Box 1334, Durban, 4001 South Africa.
⁵ Department of Microbiology, University of Stellenbosch, Private Bag X1, Matieland, 7602 South Africa.

Abstract

Two new aspartic proteases, PepAb and PepAc (encoded by pepAb and pepAc), were heterologously expressed and biochemically characterized from Aspergillus niger F0215. They possessed a typical structure of pepsin-type aspartic protease with the conserved active residues D (84, 115), Y (131, 168) and D (281, 326), while their identity in amino acid sequences was only 19.0%. PepAb had maximum activity at pH 2.5 and 50 °C and PepAc at 3.0 and 50 °C. The specific activities of PepAb and PepAc toward casein were 1368.1 and 2081.4 U/mg, respectively. Their activities were significantly promoted by Cu²⁺ and Mn²⁺ and completely inhibited by pepstatin. PepAb exhibited higher catalytic efficiency (k _cat/K _m) toward soy protein isolates than casein, while PepAc showed higher catalytic efficiency toward casein. The hydrolysis capacities of PepAb and PepAc on soy protein isolates were slightly lower than that of previously identified A. niger aspartic protease, PepA (aspergillopepsin I), while the resultant peptide profiles were remarkably different for all three proteases.

Keywords: Enzyme property; Gene cloning; Heterologous expression; Protein hydrolysis.