Part:BBa_K1674000

Secretion signal peptide originated from the B.subtilis extracellular protease AprE

Introduction

The secretion signal peptide originated from the B.subtilis extracellular protease AprE. This signal peptide routed via the Sec export-dependent pathway which described in ( figure 1 ). Proteins who intended to be secreted called exoproteins or preproteins. Preproteins of the Sec-dependent pathway need to be in a secretion-competent state during the translocation and not folded [1,2]

Figure 1 Schematic overview of the Sec-type signal peptide (SP) pathway in B.subtilis. [1] The exoprotein synthesized and directly bound to the SP and the SRP-complex (Signal Recognition Particle). The SecA protein interacts with the SRP-complex via the SP. The SRP-precursor-SecA complex move towards the membrane where the pore forming SecYEG proteins are. The SP cleaved from the precursor and the SecA-precursor complex pushed through the membrane. The SP is been degraded and the exoprotein is going through some last modification.

Design considerations

The amino acid sequence of the secretion signal peptide has been taken from an article [1]. The base pairs sequence determined by us, using the optimized codons for B.subtilis (table 1). The signal peptide was synthesized on pdr111 backbone by PCR. And the sequence was validated by sequencing after cloning in to pSB1C3.

Table 1The codons marked in yellow are the optemaized codons for B.subtilis chosen after comparing three sources marked in different colors: [4] Blue [5] red [6] purple.

Experiments and results

In order to measure the secretion abilities of this Signal peptide we cloned the signal peptide, fused to mCherry, into pdr111 plasmid (figure 2). for the ribosome binding site (RBS) we used BBa_K143021 BioBrick. We conducted a transformation of this plasmid, first to E.coli to increase the efficiency of the transformation to B.subtilis and then to B.subtilis Where it integrate into the genome, according to pdr111-trsformation-assay.

The experiment was performed according to the secretion-assay. The fluorescence from the supernatant of B.subtilis cells containing the signal peptide fused to mCherry compared to the fluorescence from the supernatant of B.subtilis cells containing only mCherry.

 

Figure 3 mCherry secretion from B.subtilis cells over time. Cells containing a signal peptide fused to mCherry or mCherry alone were centrifuged and supernatant fluorescence at excitation 587nm and emission 610nm was measured.

 

As shown in Figure 3, the supernatant fluorescence measured in cells containing the secretion signal peptide was much higher than that obtained from cells without the signal, as expected.

In both samples it can be seen that there is a mild decrease in the fluorescence, in the sample containing the signal peptide the decrease begins after reaching a fluorescence maximum. The decrease represent the natural degradation of the mCherry over time.

Figure 4 represents a logarithmic time scale of the graph shown in figure 3. This graph shows the degradation rates of the mCherry after reaching fluorescence maxima. As it can be seen, the degradation rate of the secreted mCherry is 2.5 times higher than those shown by the not secreted mCherry.

 

Figure 4 mCherry Degradation rate in a logarithmic time scale after reaching fluorescence maxima.

 

On Figure 5, it can be seen that the fluorescence of mCherry secreted by the signal peptide is 300% higher, relative to the fluorescence observed from the supernatant with no signal peptide. The results indicate that large amount of mCherry is secreted.

 

Figure 5 Signal peptide mCherry fusion fluorescence ratio to mCherry without signal peptide.

References

1. Brockmeier U (2006) New strategies to optimize the secretion capacity for heterologous proteins in Bacillus subtilis.PhD thesis, Biowissenschaften der Ruhr-Universita ̈t, Bochum
2. Kolkman, Marc A. B., René van der Ploeg, Michael Bertels, et al. 2008 The Twin-Arginine Signal Peptide of Bacillus Subtilis YwbN Can Direct Either Tat- or Sec-Dependent Secretion of Different Cargo Proteins: Secretion of Active Subtilisin via the B. Subtilis Tat Pathway. Applied and Environmental Microbiology 74(24): 7507–7513.
3. Wang, Guangqiang, Haiqin Chen, Hao Zhang, Yuanda Song, and Wei Chen 2013 The Secretion of an Intrinsically Disordered Protein with Different Secretion Signals in Bacillus Subtilis. Current Microbiology 66(6): 566–572.
4. Bacillus subtilis subsp. subtilis str. 168 [gbbct]: 1 CDS's (256 codons) "http://www.kazusa.or.jp/codon/cgi-bin/showcodon.cgi?species=224308"
5. Moszer, I., Rocha, E. P., & Danchin, A. (1999). Codon usage and lateral gene transfer in Bacillus subtilis. Current opinion in microbiology, 2(5), 524-528.
6. JAVA CODON ADAPTATION TOOL "http://www.jcat.de"

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]