Difference between revisions of "Team:USP UNIFESP-Brazil/Description"

Spider silk is an amazing bionanomaterial due to its exceptional features. It exhibits high tensile strength, high fracture resistance, high elasticity and it has biocompatibility and low degradability. Some studies show silk can be compared to a synthetic polymer called Kevlar, that is made of aramid and is used to make body armor (Lewis). Silks are polymers composed of proteins. These proteins and their genes present specific repetitive sequences that are associated with silk properties, making it possible to handle it in order to obtain the most suitable material for each application. Moreover, some studies suggest that the terminal domains of silk proteins play important roles in the polymerization process. In this way, it can be possible to add N- and C- terminal domains in several interesting proteins or motifs and spun it with native proteins to obtain a customized silk.

The size of genes, their repetitive sequences and high content of Cytosine and Guanine establish a challenge to many expression systems. However Chlamydomonas reinhardtii has naturally high CG content on its genome and it could be able to deal with this problem, it can also perform post translational modifications and it can secrete complex proteins, easing the purification process. Furthermore, it exhibits low cost production, rapid growth, scalability and stable transgenic line generation, all desired characteristics to an expression system (Wijffels, Kruse, and Hellingwerf; Rosenberg et al.). It is important to highlight the low cost of microalgae cultivation, while production of antibodies in mammalian cells presents an average cost about US$150.00/per gram of raw materials and plants US$0.05/per gram (Dove), Maylfield has estimated that microalgae can reach US$ 0.002/liter (Rosenberg et al.; Mayfield, Franklin, and Lerner). Chlamydomonas reinhardtii also is Generally Recognized As Safe (GRAS), that is, it has low risk of being contaminated by virus, prions and bacterial endotoxins (Mayfield et al.). Easy purification and low risk of contamination are very significant issues when we are talking about making products to biomedical applications.

Figure 1. Cassette construction to be inserted in C. renhardtii nuclear genome. Promoter hsp70A/rbcs2: fusion of the promoters hsp70A and rbcs2 (Eichler-Stahlberg et al.; Schroda, Blöcker, and Beck). Sh-Ble: resistance gene to Zeomycin. 2A: self-cleavage peptide from Foot and Mouth Disease Virus (FMDV) (Rasala et al.). SP: secretion signal peptide of the gene Ars1. GOI: gene of interest. His: histidine tag. RbcS2 3’ UTR: terminal sequence of the gene RbcS2 (Fuhrmann et al.). Introns were added as the figure shows (Eichler-Stahlberg et al.; Lumbreras et al.).

Our project was inspired by the UCLA’s projects presented at iGEM in 2014 and 2015 about synthetic silks. Like we said above, silks are very interesting material but one of the main problems is dealing with its high content of Cytosine and Guanine. Most of the expression systems are not able to deal with that, however we have known Chlamydomonas reinhardtii has naturally high CG content which makes it interesting as an expression chassis. One of UCLA’s projects was called Silk Functionalization: Developing the Next Generation of Performance Fibers. The team has created a genetic construct using the Green Fluorescent Protein (GFP) inserted between N- and C- terminal domains of Bombyx mori’s silk to express proteins able to bind to native silk proteins. When this customized GFPs and native proteins were mixed and spun they were able to recognize each other by the terminal domains, making a fluorescent silk.

From this idea we thought: “Silk is a very interesting material and could be expressed in Chlamydomonas reinhardtii, a model organism that has many advantages and that remains underexplored. What could be put in place of a GFP to express in microalgae? What biomolecule could take advantage of this amazing silk feature? It has to work while immobilized... Why not enzymes? There are many studies about enzymes immobilization, enzymes are very appropriate and useful in many applications around the world!”. But we knew it could not to be any enzyme linked to silk, we knew it need to address technical, social and economic issues. So we read that spider silk has been studied to many biomedical applications, like the treatment of burn victims. Then we studied about burns in order to find an interesting enzyme that could solve some problem and we learned that one of the most important problems affecting burn victims is sepsis. In this way, we sought for antimicrobial enzymes and we found the endolysins. Endolysins are very interesting enzymes because they are able to combat multiresistant bacterias and they are specific, avoiding problems like the antibiotic resistance.

So we decided to make a project about spider silk production in microalgae, creating possibilities to future works with silk proteins from this amazing organism model, like the association between them and endolysins by UCLA’s approach in order to make an antimicrobial silk to be applied on burn victims to combat sepsis.

One challenging part of working with a new chassis is the development of new tools and parts. In order to access the efficiency of protein expression, reporter genes are the state-of-the-art. With that in mind, we decided to improve the characterization of mCherry (BBa_J06504), a robust fluorescent protein, perfect for accessing the efficiency of expression systems (such as ours!) as well as characterizing promoters, terminators and signal peptides. We further characterize this reporter by expressing and codon optimizating it in a new Chassis Chlamydomonas reinihardtii.The full data about our improvements in characterization and function can be found here.

The first improvement in characterization we made was using Fast Protein Liquid Chromatography (FPLC) to analyse and purify our mCherry. FPLC is an Ion exchange purification that exploit the net electrostatic charges of proteins, in pH values different of their pI (Isoelectric point). We developed a purification protocol to mCherry. First, we performed a gradient purification to establish the best salt concentration to elute mCherry.

Gradient Set Up:

We obtained the following result (Figure 7).

Figure 2. Chromatogram of gradient mCherry purification. Green line (-) is the UV sensor reading. Red line (-) is buffer B percentage in the mixture. Black line (-) is the conductivity measurement. Blue line (-) is the fluorescence measurement of fractionated samples.

UV absorbance curve integration allow us to estimate the amount of protein separated from mCherry, 99% of all protein detected by the sensor was separated from mCherry fractions.

The samples purified from this method were used to further characterize our mCherry produced by Chlamydomonas reinhardtii. The Excitation/Emission spectrum (Figure 9) obtained are similar to the ones available to mCherry.

Figure 3. Spectra of excitation and emission for C. reinhardtii expressed, codon optimized mCherry

Eichler-Stahlberg, Alke et al. “Strategies to Facilitate Transgene Expression in Chlamydomonas Reinhardtii.” Planta 229.4 (2009): 873–883. Print.

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Rasala, Beth A. et al. “Robust Expression and Secretion of Xylanase1 in Chlamydomonas Reinhardtii by Fusion to a Selection Gene and Processing with the FMDV 2A Peptide.” PloS one 7.8 (2012): e43349. Print.

Rosenberg, Julian N. et al. “A Green Light for Engineered Algae: Redirecting Metabolism to Fuel a Biotechnology Revolution.” Current opinion in biotechnology 19.5 (2008): 430–436. Print.

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Wijffels, René H., Olaf Kruse, and Klaas J. Hellingwerf. “Potential of Industrial Biotechnology with Cyanobacteria and Eukaryotic Microalgae.” Current opinion in biotechnology 24.3 (2013): 405–413. Print.