Part:BBa_K4275040

pLAC4-KmarxMFα-TrEGIII-t-tTDH1

The composite part is composed of Kluyveromyces marxianus mating factor alpha[2](BBa_K4275000) and endoglucanase TrEGIII-t fused with type 1 dockerin [3](BBa_K4275006).

Kluyveromyces marxianus mating factor alpha (BBa_K4275000) is fused for the purpose of secretion of target enzyme TrEGIII-t, which would then be anchored on CipA1B2C scaffold protein by type I cohesin-dockerin interaction and assembled into the cellulosome complex.

The part is a crucial component for effective cellulose decomposition.

Usage and Biology

Kluyveromyces marxianus mating factor alpha is a secretion signal in Kluyveromyces marxianus. The MFa encodes for an alpha mating factor domain that is fused with TrEGIII-t. The translation of this signal peptide found on the MFa domain causes the polypeptide to enter RER and Golgi body and allows the target enzyme to be secreted by Kluyveromyces marxianus.

TrEGIII-t is type of endo-1,4-beta-endoglucanase with type I dockerin fused to its C terminal. The enzyme functions by hydrolyzing internal glycosidic bonds in cellulose chains to generate new free ends that CBH can acts on. TrEGIII-t, CBHII-t, and NpaBGS-t works collectively with the assistance of two cellulase boosters to achieve a highly-efficient degradation of cellulose in waste textiles.

Characterization

Cellulases and cellulase boosters expression

The enzymatic digestion of the polysaccharide chains of cellulose was completed by exoglucanase, endoglucanase and 1-4 betaglucosidase, and this series of reactions are catalysed by LPMO and CDH. We constructed expression vectors for yeast Kluyveromyces marxianus with the unique origin of replication and antibiotic selection marker for the culturing of Kluyveromyces marxianus. Expression vectors were made distinct by the insertion of different sequences coding for the ligated form of the cellulase enzymes, LPMO and CDH. The enzymes were ligated with an alpha-mating factor secretion signal for Kluyveromyces marxianus at the N-terminus and a type I dockerin domain at the C-terminus (Fig.1A).The successful production and secretion of the protein NpaBGS, MtCDH and TrEGIII are examined by SDS-PAGE and western blot analysis (Fig.1D).

Figure 1: Fig.1 Construction of expression vectors for fusion proteins production in yeast Kluyveromyces marxianus and the analysis of the secreted enzymes (A) The design of our expression vector for production of cellulases and cellulase boosters in Kluyveromyces marxianus; the coding sequences for the cellulases and cellulase boosters were ligated with an alpha-mating factor secretion signal for Kluyveromyces marxianus at the N terminus and a type I dockerin domain at the C terminus linked by a flexible linker (B) The growth curve of recombinant yeasts transformed with expression plasmids coding for different enzymes (C) The agarose gel electrophoresis image of coding sequences for different enzymes, respectively NpaBGS, TaLPMO, CBHII, MtCDH and TrEGIII (D) Western blot result for TrEGIII and MtCDH.

Cellulosome construction

We assembled the cellulose-like complex on the surface of E.coli by adding primary scaffold proteins, cellulases and cellulase boosters onto E.coli expressing secondary scaffold proteins. The mixture was centrifuged and resuspended in tris-HCl. The mixture underwent centrifugation and resuspension using tris-HCl, and cellulose was added to the mixture. After 24h, the mixture was filtered and tested for glucose by Benedict's test. From the result, we determined that the cellulosome-like complexes are able to degrade cellulose at a higher efficiency than cell-free cellulases mixture (Fig.2A and 2B). The overall success in engineering our project was verified by the successful construction of cellulosome complex and degrading cellulose to reducing sugars.

Figure 2: Fig.2 The Benedict’s quantitative and qualitative tests for reducing sugar produced by the enzymatic or cellulosomal degradation of cellulose (A) Benedict’s qualitative test result for reducing sugar production through 24h of cellulose degradation by cellulosome, cellulosome without boosters, nanobody presenting cell+free cellulases+cellulase boosters, nanobody presenting cell+cellulases and nanobody presenting cell control from left to right (B) Benedict’s quantitative test for absorbance of the samples obtained from the Benedict’s qualitative test at 635 nm wavelength.

Sequence and Features

Assembly Compatibility:

• 10
  INCOMPATIBLE WITH RFC[10]

  Illegal EcoRI site found at 331
  
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal EcoRI site found at 331
  Illegal NheI site found at 89
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal EcoRI site found at 331
  Illegal XhoI site found at 1252
  Illegal XhoI site found at 2830
  
• 23
  INCOMPATIBLE WITH RFC[23]

  Illegal EcoRI site found at 331
  
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal EcoRI site found at 331
  Illegal AgeI site found at 1603
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal SapI site found at 1475
  

References

1. Rajkumar, Arun S. et al. "Biological Parts For Kluyveromyces Marxianus Synthetic Biology". Frontiers In Bioengineering And Biotechnology, vol 7, 2019. Frontiers Media SA, https://doi.org/10.3389/fbioe.2019.00097.
2.“Mating Factor Alpha-1 [Kluyveromyces Marxianus] - Protein - NCBI.” National Center for Biotechnology Information, U.S. National Library of Medicine, https://www.ncbi.nlm.nih.gov/protein/QGN17207.1
3. Chang, Jui-Jen et al. "PGASO: A Synthetic Biology Tool For Engineering A Cellulolytic Yeast". Biotechnology For Biofuels, vol 5, no. 1, 2012. Springer Science And Business Media LLC, https://doi.org/10.1186/1754-6834-5-53.
4. "Part:Bba K2753052 - Parts.Igem.Org". Parts.Igem.Org, 2022, https://parts.igem.org/Part:BBa_K2753052.