Tent of synthesized gene was kept within 1516647 45?5 ; 4) to prevent the exhaustion of frequently used tRNA, the codons of some amino acids, such as Leu, Thr, Ala and Gly, were replaced by the second or third high-frequency codons. For example, although the highest frequency codon for Leu is TTG (31.9), the usage frequency for other two degenerate codons CTT (16.1) and CTG (15.5) was still acceptable. When we met the amino acid sequence block such as FML98N and YL229FN (Fig. 1), if we always select the highest-frequency codon for each amino acid (Table S8), the nucleotide sequences will become 59TTTATGTTGAAC-39 and 59-TACTTGTTTAAC-39, respectively. So in order to make the four nucleotides dispersing in the sequence evenly and also to make the GC content within 45 ?Expression in P. pastorisThe premature CALB contains three parts, N-terminal signal peptide, pre-sequence and mature enzyme (Fig. 1B). In order to obtain a recombinants with the highest expression capacity, the factors MedChemExpress SPDP including the codon usage frequency, signal peptide, presequence and constitutive or inducible expression were considered. We constructed a series of recombinants and comparatively analyzed their lipase production capacity using 
tributyrin-MS plates and flask fermentation (Fig. 3A). The 
lipases were expressed as a glycosylized secreting proteins from both the original and synthesized genes with the size of 37 kDa, and after deglycosylation by Endo H the size becoming 35 kDa (Fig. 3B). The secretion capacity of a-factor signal peptide was significantly stronger than that of the original signal peptide. For example, the lipase activity of the recombinants pPIC3.MedChemExpress Indolactam V 5KCalBSP and pPIC9K-CalBP were 65.2 U/mL, 69.8 mg/L respectively. Howerer, the pre-sequence can retard the CALB expression as showed by pPIC9K-CALBP and pPIC9K-CALB. The recombinants carrying the codon-optimized a-factor signal peptide and CALB gene (pPIC9KaM-CalBM and pGAPZaCalBM) demonstrated a much stronger lipase secretion capacity than the transformants with original gene (pPIC9K-CalB,High-level Expression of CALB by de novo DesigningFigure 2. in vitro synthesis of a-factor, native CALB and codon-optimized CALB genes. A single-step strategy (A-PCR) was conducted to synthesize the codon-optimized a-factor (A and B), and a two-step strategy combining A-PCR and OE-PCR (C) was conducted to synthesize the native CALB (D) and codon-optimized CALB (E) genes. In order to synthesize the native CALB, the oligonucleotides were firstly 15755315 assembled into F1 (541 bp) and F2 (510 bp), and then they were assembled into the genes with native signal peptide (CalBSP), native pre-sequence (CalBP) and mature CALB (CalB) with different primer pairs at OE-PCR step (D). In order to synthesize the codon-optimized CALB, the oligonucleotides were firstly assembled into F1M (510 bp) and F2M (553 bp), and then they were assembled into genes with signal peptide (CalBSPM), pre-sequence (CalBPM) and mature CALB (CalBM) with different primer pairs at OE-PCR step (E). doi:10.1371/journal.pone.0053939.gpPIC9KaM-CalB, pGAPZa-CalB). The highest activity was obtained from the methanol-inducible, codon-optimized a-factor and CALB co-expressed recombinant pPIC9KaM-CalBM. After the inducible expression for 96 h, both the lipase activity and protein content in the broth reached their maximal levels of 210.7 U/mL and 155.5 mg/L, respectively. In contrast, recombinants (pPIC9K-CalB) carrying the original gene had only 120.2 U/mL and 98.7 mg/L, respectivel.Tent of synthesized gene was kept within 1516647 45?5 ; 4) to prevent the exhaustion of frequently used tRNA, the codons of some amino acids, such as Leu, Thr, Ala and Gly, were replaced by the second or third high-frequency codons. For example, although the highest frequency codon for Leu is TTG (31.9), the usage frequency for other two degenerate codons CTT (16.1) and CTG (15.5) was still acceptable. When we met the amino acid sequence block such as FML98N and YL229FN (Fig. 1), if we always select the highest-frequency codon for each amino acid (Table S8), the nucleotide sequences will become 59TTTATGTTGAAC-39 and 59-TACTTGTTTAAC-39, respectively. So in order to make the four nucleotides dispersing in the sequence evenly and also to make the GC content within 45 ?Expression in P. pastorisThe premature CALB contains three parts, N-terminal signal peptide, pre-sequence and mature enzyme (Fig. 1B). In order to obtain a recombinants with the highest expression capacity, the factors including the codon usage frequency, signal peptide, presequence and constitutive or inducible expression were considered. We constructed a series of recombinants and comparatively analyzed their lipase production capacity using tributyrin-MS plates and flask fermentation (Fig. 3A). The lipases were expressed as a glycosylized secreting proteins from both the original and synthesized genes with the size of 37 kDa, and after deglycosylation by Endo H the size becoming 35 kDa (Fig. 3B). The secretion capacity of a-factor signal peptide was significantly stronger than that of the original signal peptide. For example, the lipase activity of the recombinants pPIC3.5KCalBSP and pPIC9K-CalBP were 65.2 U/mL, 69.8 mg/L respectively. Howerer, the pre-sequence can retard the CALB expression as showed by pPIC9K-CALBP and pPIC9K-CALB. The recombinants carrying the codon-optimized a-factor signal peptide and CALB gene (pPIC9KaM-CalBM and pGAPZaCalBM) demonstrated a much stronger lipase secretion capacity than the transformants with original gene (pPIC9K-CalB,High-level Expression of CALB by de novo DesigningFigure 2. in vitro synthesis of a-factor, native CALB and codon-optimized CALB genes. A single-step strategy (A-PCR) was conducted to synthesize the codon-optimized a-factor (A and B), and a two-step strategy combining A-PCR and OE-PCR (C) was conducted to synthesize the native CALB (D) and codon-optimized CALB (E) genes. In order to synthesize the native CALB, the oligonucleotides were firstly 15755315 assembled into F1 (541 bp) and F2 (510 bp), and then they were assembled into the genes with native signal peptide (CalBSP), native pre-sequence (CalBP) and mature CALB (CalB) with different primer pairs at OE-PCR step (D). In order to synthesize the codon-optimized CALB, the oligonucleotides were firstly assembled into F1M (510 bp) and F2M (553 bp), and then they were assembled into genes with signal peptide (CalBSPM), pre-sequence (CalBPM) and mature CALB (CalBM) with different primer pairs at OE-PCR step (E). doi:10.1371/journal.pone.0053939.gpPIC9KaM-CalB, pGAPZa-CalB). The highest activity was obtained from the methanol-inducible, codon-optimized a-factor and CALB co-expressed recombinant pPIC9KaM-CalBM. After the inducible expression for 96 h, both the lipase activity and protein content in the broth reached their maximal levels of 210.7 U/mL and 155.5 mg/L, respectively. In contrast, recombinants (pPIC9K-CalB) carrying the original gene had only 120.2 U/mL and 98.7 mg/L, respectivel.
