Substrate scope of PmiLAAD
The catalytic efficiency of Pmi LAAD toward
13 L-amino acids was investigated and
the results are illustrated in Supplementary Table 1. Efficiency was
dictated by the amino acids’ R groups: the highest catalytic activity
was observed in long-chain aliphatic amino acids, such as L-Leu (100%)
and L-Ile (96.9%), followed by the sulfur-containing L-Met (73.5%),
short-chain aliphatic L-Val (66.3%), aromatic L-Phe (54.1%),
positively charged L-Arg (28.2%), and negatively charged L-Glu (8.6%).
Hardly no catalytic activity was detected toward amino acids containing
a hydroxyl group, such as L-Ser and L-Thr. Six amino acids with diverse
R groups (L-Leu, L-Met, L-Val, L-Phe, L-Arg, and L-Glu) were selected
for further experiments. When 100 g/L of L-Leu, L-Met, L-Val, L-Phe,
L-Arg, and L-Glu were transformed by 10 g/L of whole-cell catalyst
(Pmi LAAD), the titer of the corresponding α-keto acids was 98.2,
72.1, 65.3, 53.2, 27.6, and 8.4 g/L, respectively (Figure 1B). These
values indicated that there was space for improving Pmi LAAD
catalytic efficiency through protein engineering.