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Engineering protonation conformation of l ‐aspartate‐α‐decarboxylase to relieve mechanism‐based inactivation
Author(s) -
Qian Yuanyuan,
Lu Cui,
Liu Jia,
Song Wei,
Chen Xiulai,
Luo Qiuling,
Liu Liming,
Wu Jing
Publication year - 2020
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.27316
Subject(s) - protonation , chemistry , stereochemistry , catalysis , fumaric acid , alanine , substrate (aquarium) , aspartic acid , enzyme kinetics , substrate specificity , biochemistry , active site , enzyme , amino acid , biology , organic chemistry , ion , ecology
Mechanism‐based inactivation of l ‐aspartate‐α‐decarboxylase (PanD), which leads to irreversible modification of active site, is a major challenge in the efficient production of β‐alanine from L ‐aspartic acid. In this study, a semi‐rational strategy that combined conformational dynamics and structural alignment was applied to increase the catalytic stability of Bacillus subtilis PanD ( BsPanD ). Using site‐saturation and C‐terminal deletion, the variant Q5 ( Bs PanD I46V/I88M/K104S/I126* ) was generated. The catalytic half‐life and the total turnover number (TTN) of Q5 were 3.48‐fold and 2.52‐fold higher, respectively, compared with that of the parent Q0. The reasons for the differences were the prolonged distance d1 between the phenolic group of Tyr58 and pyruvoyl group of Ser25 (4.9 Å in Q0 vs. 5.5 Å in Q5), an increased difficulty for incorrect protonation to occur, and the decreased flexibility of residues in regions A, B, and C, thereby enhancing the probability of correct protonation. Variant Q5, coupled with l ‐aspartase (AspA) in a 15‐L bioreactor, generated a linear cascade system using fumaric acid as a substrate, yielding 118.6 g/L β‐alanine with a product/catalyst (P/C) ratio of 5.9 g/g and a conversion > 99%. These results showed that reshaping the protonation conformation of PanD can efficiently relieve mechanism‐based inactivation and boost catalytic stability.