Revision as of 12:42, 13 October 2022

pLAC4-KmarxMFα-TaLPMO-t-tTDH1

The composite part includes K. marx mating factor alpha[2] (BBa_K4275000) and cellulase booster TaLPMO-t[3] fused with type I dockerin for the assembly of cellulosome complex.

The fusion of K. marx mating factor alpha is used in order for the target TaLPMO-t cellulase booster to be secreted from our host yeast, which would be anchored on scaffold protein and assembled into the cellulosome complex.

Usage and Biology

Kluyveromyces marxianus mating factor alpha act as a secretion signal in Kluyveromyces marxianus. The mating factor alpha fuses an alpha mating factor domain onto TaLPMO-t. The signal peptide on the domain would direct the TaLPMO-t into RER and Golgi body, enabling the designated cellulase booster to be secreted by Kluyveromyces marxianus.

TaLPMO-t is a cellulase booster with type I dokerin fused on its C terminal to convert the protein from free booster enzyme into cellulosomal mode. As a copper-dependent enzyme, TaLPMO-t oxidizes and cleaves glycosidic bonds in cellulose, which significantly boosts the efficiency of crystalline cellulose degradation.

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

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. Harris, Paul V. et al. "Stimulation Of Lignocellulosic Biomass Hydrolysis By Proteins Of Glycoside Hydrolase Family 61: Structure And Function Of A Large, Enigmatic Family". Biochemistry, vol 49, no. 15, 2010, pp. 3305-3316. American Chemical Society (ACS), https://doi.org/10.1021/bi100009p.
4. "Part:Bba K2753052 - Parts.Igem.Org". Parts.Igem.Org, 2022, https://parts.igem.org/Part:BBa_K2753052.