Fig. 1

Schematic illustration of proteins or vectors. a Schematic illustration of the Subtilisin QK-2 protein. SP signal peptide; P propeptide; M mature peptide. b Schematic illustration of secretory expression vectors. P _nisA promoter; SPusp secretion signal sequence for L. lactis; qk (b-1) wild-type gene; qk′ (b-2) the entire gene sequence with codon optimization; qkpro’ (b-3) the only codon-optimized propeptide gene sequence. (b-1) contains plasmids pRF02, pRF02H, pRF03 and pRF03H. (b-2) indicates plasmid pRF04H. (b-3) indicates plasmid pRF05H. c Schematic illustration of the AcmA protein. S.S. signal sequence; A.D. active domain; LysM anchoring repeats; d schematic illustration of vectors for surface display. (d-1), (d-2), (d-3) and (d-4) indicate plasmids pRF06H, pRF07H, pRF08H and pRF09H, respectively. pRF02 and pRF02H were selected by the complementation of the lacF gene and others were selected by the chloramphenicol resistant gene. H his-tag