Sequence and Features

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Introduction

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Figure 1. Mechanism of action. The CBDcipA-fusion is attached to cellulose. By adding thrombin from any source the fusion protein will be cleaved and the C-terminal fusion protein will be released into the solution. By changing the fusion protein to an antimicrobial peptide/enzyme, and using the cellulose as a bandage, the peptide/enzyme can be released into a wound by native human thrombin.

This part consists of a cellulose binding domain (CBD) from Clostridium thermocellum (C. thermocellum) cellulose scaffolding protein (CipA) and is a central part Clostridium thermocellum's cellusome. The CBD was fused to sfGFP in this part to easily track the binding capacities and to test our release mechanism. The CBD-sfGFP were fused using a flexible GS-linker (-GGGGSGGGGS-). A thrombin cleavage site (-LVPRGS-) was added to the end of the linker and its breakage will leave a glycine and serine attached to the N-terminal of the sfGFP fusion protein.

Assembly compabilities

An internal BamHI recognition sequence (RS) has been added to enable changeable fusion proteins. BamHI was chosen because its RS codes for glycine and serine, fitting it to the end of the thrombin site. It is also cost-effective enzyme and is unaffected by methylated DNA.

This part can be used to track purification, measure CBD binding ability and report cleavage at the thrombin site.

CBDcipA crystal structure

Figure 1. Crystal structure of CBDcipA with a resolution of 1.75 Å which were solved by [http://www.ncbi.nlm.nih.gov/pmc/PMC452321 Tormo et al. 1989]. PDB code 1NBC. In red from the left, W118, R112, D56, H57 and Y67, thought to be the surface which interacts strongly with cellulose.

Important molecular faces

CBDcipA is composed of a nine-stranded beta sandwich with a jelly roll topology and binds a calcium ion. It further contains conserved residues exposed on the surface which map into two clear surfaces on each side of the molecule. One of faces mainly contains planar strips of aromatic and polar residues which may be the cellulose binding part. Further aspect are unknown and unique with this CBD such as the other conserved residues which are contained in a groove.

The choice of cellulose binding domain

iGEM Linköping 2019 choose CBDcipA due to many other iGEM teams exploring the possibilities of this domain. Our basic design was influenced by iGEM14 Imperial, iGEM15 Edinburgh and iGEM18 Ecuador. Purification and where to place the fusion protein (N- or C-terminal) was determined by studying the former projects. CBDcipA also originates from a thermophilic bacteria which further increases the domains applications.

Figure Y. Mechanism of action

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