Part:BBa_K4011000

CBM3

CBMs are artificial proteins derived from natural proteins with cellulose-binding functions, such as cellulase. There are three types of CBMs, which are CBMs, CBM1, CBM2, and CBM3. CBM1 is the smallest, whilst CBM3 is the biggest. By fusing CBMs to functionalization proteins, we can achieve modification/functionalization of our bacterial cellulose membrane. This is part in a part collection where we characterize bacterial cellulose modification methods and constructs using CBMs.

The part collection includes: Cellulose binding matrix BBa_K4011000 and BBa_K4011001. CBMs fused with spider silk fibroin BBa_K4011000 and BBa_K4011009. Fused proteins capable of expression and secretion in <S. cerevisiae> BBa_K4011010 and BBa_K4011011.

This part collection can help and inspire other teams we are trying to achieve modification of cellulose membranes using different modification/functionalization proteins.

Usage and Biology

In nature, CBM3s are expressed as a domain of a protein whose functions require being bound to cellulose, such as cellulase. The structure of CBM3 is displayed in the Characterization section (Protein Data Bank accession: 1NBC).

CBM3 fused with spider silk proteins is first done by Mohammadi et al in 2019, where they tested the changes in physical properties on cellulose fibers after mixing with CBM3-spider silk.

Characterization

In order to modify BCM’s physical properties, we designed and expressed spider silk fibroins fused with cellulose binding matrixes (CBMs; learn more on our description page) to bind to BCM (Fig. 1). For our project, we experimented with CBM3 from Ruminiclostridium thermocellum (Protein Data Bank (PDB) accession: 1NBC; Fig. 5D) (2) and CBM2 from Cellulomonas fimi (PDB accession: 1EXG; Fig. 5C). For our spider silk protein, we chose to use the synthetic mini spider silk protein NT2RepCT (2Rep; first characterized by GreatBaySZ_2019). 2Rep is water-soluble due to hydrophilic interactions of protein N-terminal and C-terminal. When 2Rep is submerged in a coagulating bath and subjected to a shear force, the repetitive regions will uncoil, form beta-pleated sheet networks and solidify into silk fiber (Fig. 1A).

For adding CBM3 flanking to 2Rep, we synthesized CBM3-BsaI-CBM3 on a pET28a vector. Primers were then used to add BsaI restriction sites in 2Rep to fuse the respective domains together in the synthesized pET28a vector by Golden Gate assembly (Fig. 2A & 2B). After construction, the plasmids were transformed into E. coli BL21(DE3) for IPTG-inducible expression (Fig. 2C).