RESEARCH ARTICLE
Screening and Characterization of a Mutant Fungal Aspartic Proteinase from Mucor pusillus
Li Yuqiu, Tan Hua, Li Da, Li Zhoulin, Chi Yanping, Jiang Yuanyuan, Liu Xiangying, Wang Jinghui*, Li Qiyun*
Article Information
Identifiers and Pagination:
Year: 2015Volume: 9
First Page: 119
Last Page: 126
Publisher ID: TOBIOTJ-9-119
DOI: 10.2174/1874070701509010119
Article History:
Received Date: 17/02/2014Revision Received Date: 21/03/2015
Acceptance Date: 09/06/2015
Electronic publication date: 10/9/2015
Collection year: 2015
open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Abstract
In this study, site-directed mutagenesis was carried out to alter properties of Mucor pusillus rennet (MPR) in order to find a potential substitution of commercial chymosin. Mutant G186D/E13D screened from thousands of mutants showed a significant milk-clotting activity (MCA). Mutant G186D/E13D rennet was purified and characterized. The molecular weight was estimated to be 44 kDa by SDS-PAGE. The maximum enzyme activity was at a wide range of pH (5.0-7.0) and 60ºC. The enzyme was inhibited by metal ions (Fe2+, Fe3+, Cu+ and Zn2+), 1.10-Phenantrolin and pepstatin A. Further texture analysis of types of cheddar cheese made by non-mutant rennet, mutant (G186D/E13D) rennet and commercial rennet suggested that the soluble nitrogen content and hardness of cheddar cheese made by chimeric mutant rennet was decreased without any significant change in flavor between these cheeses. The result implicated that, to some extent, the mutant rennet could decrease hydrolysis of protein during ripening of cheese, probably as a candidate for a useful milk coagulant.