Table 1 Residues with important roles identified in the AAT family

H166A, D170A, D170N, D170E and S34A

VpAAT

H166A and S34A, D170A and D170N changed the solvent channels in the structure, with no activity for the mutants

[59]

Y52F, D381A and D381E

VpAAT

The binding ability to several substrates was significantly reduced, and D381 and Y52 played a crucial role in maintaining the solvent channel structure

[63]

Y20F, F97W and A138T

CATs

Mutants weaken the interaction between chloramphenicol, H189, and Y20 at the transition state, to improve the promiscuous activities of CATs. Mutants Y20F and F97W improved the promiscuity of CATs towards smaller alcohols and thermostability, but the combinatorial mutations did not result in beneficial effects synergistically

[75, 77, 78]

S405A

CaAT20

The S405A mutant of CaAT increased the volume of enzyme binding cavity, enhanced the affinity with geraniol and thus improved the enzyme activity

[80]

H165V, A170S, A174S, L177T, S262A, F264Y, K298F, F314Y, R339V, K342F, S375A, D376A, H379V, F382Y

PpAAT

Among the 14 candidate amino acid residues, substitutions of S262, F264, and S375 did not cause any significant effect on the enzymatic activities of PpAAT. Substitutions of all 11 candidate amino acid residues possibly involved in the internal esterification reaction dramatically decreased the enzymatic activities of PpAAT, especially the substitutions of H165 and D376, which led to total loss of enzymatic activities

[67]

L41T, F43T, F45T, D169A, R360V, R362V, F372T

PpAAT

Among the 7 candidate amino acid residues, the substitution of F43 did not cause any significant effect on K_cat/K_m of the site-directed mutant protein. However, substitutions of all the other 6 candidate amino acid residues dramatically decreased K_cat/K_m of the mutant proteins

[67]

S99G, F185I, L178F

AcAAT

The S99G and L178F mutants produced 4.5-fold and 1.9-fold butyl octanoate compared to WT, respectively, while the L178F mutant produced significantly less butyl butyrate

[72]