Engineering an Escherichia coli surface display platform based on an autotransporter from Stenotrophomonas maltophilia: Autodisplay of enzymes with low to high molecular weight

Surface display technology has garnered significant attention for preparing efficient whole cell catalysts, while reported carrier proteins still cannot meet the demand to display various passenger domains, especially for those with high molecular weight. This study demonstrates that the autotransporter of esterase Est7 (E7AT) from Stenotrophomonas maltophilia played a decisive role in its efficient surface display. Guided by the original signal peptide, the surface display ratio of Est7 was determined as 89.67 % with the total enzymatic activity of 16.67 U/mL, which was much higher than 4.60 U/mL and 5.70 U/mL for the signal peptides derived from pectolase B (pelB) and cholera toxin B (ctxB), respectively. Then, the E7AT unit was successfully developed to surface display proteins with varying molecular weight from 19.3 kDa to 117.9 kDa, showing a more effective autodisplay ability than adhesin involved in diffuse adherence (AIDA-I), ice nucleation proteins (InaK and InaP), and outer membrane proteins (lipoprotein/ompA, MltA-interacting protein A, and yiaT) systems. Additionally, a galactosidase (GAL) displayed by E7AT was employed to hydrolyze lactose, achieving a promising hydrolysis rate of 31.63 % in 2 h. The displayed GAL retained 63.24 % and 41.41 % activity in third and sixth batch, respectively, indicating the considerable potential of E7AT in developing efficient whole cell catalysts.