User:Polymer33/sandbox

Elastin like polypeptides:

This is a very interesting topic, as it bridges key concepts of polymer chemistry and synthesis with biomedical applications, particularly those involving phase-based protein purification via temperature change as well as drug therapy and more efficient drug delivery. The article itself only begins to introduce elastin like polypeptides by mentioning its general structure (VPGXG)n, how the identity of the "X" or the variable amino acid will change the transition temperature (temperature above which the pentapeptide polymer will aggregate and below which the pentapeptide will solubilize), and how it may be used in purification and in drug therapy. My work will be to expand on these topics with clear examples involving specific research groups which have experimental data supporting these applications. Also, I will add the topic of elastin like polypeptide use in hydrogel formation as well as the importance of charged residues for the determination of the transition temperature of the pentapeptide.

Roberts, S; Dzuricky, M; Chilkoti, A (14 September 2015). "Elastin-like polypeptides as models of intrinsically disordered proteins". FEBS Letters. 589 (19): 2477–2486. doi:http://doi.org/10.1016/j.febslet.2015.08.029. Retrieved 13 April 2017.

In this source, a relationship is established between the ELPs and intrinsically disordered proteins. IDPs are correlated with the presence of "elastic" ELPs that have not folded into their native confirmation. Also, the importance of the variable "X" residue is established as increasing the hydrophobicity of the "X" residue leads to an increase in the proportion of ELPs assuming the compact global state. Hence, the authors propose there may be a relationship between decreasing hydrophobicity and increasing similarity to IDPs.

Hassouneh, W; Christensen, T; Chilkoti, A (August 2010). "Elastin-like polypeptides as a purification tag for recombinant proteins". Current Protocols in Protein Science. doi:10.1002/0471140864.ps0611s61.. PMID 20814933. Retrieved 13 April 2017.

This article is important in that it brings up the potential use of ELPs in protein purification. The key here lies in the temperature-based phase transition associated with ELPs. Above the critical temperature, the ELPs clump together and below this temperature, the ELPs go back into the solution. Using this characteristic, the group in this paper was able to come up with a general procedure using ELPs in protein purification. Initially, the ELP is modified so that it contains a functional group that binds to the protein of interest. By increasing the temperature of the solution, clumps form, and the protein-ELP conjugate forms in the pellet during centrifugation. The supernatant is removed and the same procedure is repeated, but now with a cold temperature so that the aggregates can go back into the solution. A cycle of cold spins and hot spins will lead to a very pure concentration of the original protein without destroying the ELP as the ELP undergoes a reversible transition.

Christensen, T; Hassouneh, W; Trabbic-Carlson, K; Chilkoti, A (2013 March 25). "Predicting Transition Temperatures of Elastin-Like Polypeptide Fusion Proteins". Biomacromolecules. 14 (5): 1514–1519. doi:10.1021/bm400167h. Retrieved 13 April 2017.

The original stub article focused on the importance of hydrophilic and hydrophobic residues in determining the temperature at which ELPs undergo fusions and become polymers. In this study, addition of a charged residue to the ELP motif seems to dramatically affect the probability that free ELP monomeric units will polymerize. The contribution of each amino acid to polymerization was measured using two different parameters- the ability of the amino acid to be exposed to the solvent as well as the amino acid impact on transition temperature. The group concluded that, while the charged amino acids were not exposed significantly more to solvent, they had a much higher sequence-specific impact on the transition temperature.

Glassman, MJ; Avery, RK; Khademhosseini, A; Olsen, BD (20 January 2016). "Toughening of Thermoresponsive Arrested Networks of Elastin-Like Polypeptides To Engineer Cytocompatible Tissue Scaffolds". Biomacromolecules. 17 (2): 415–426.  doi:10.1021/acs.biomac.5b01210. Retrieved 13 April 2017

This article is significant as it establishes a capacity of ELP polymers in regenerative biology through the formation of stiff hydrogels that can support the growth of chondrocytes. The ELP polymers themselves aggregate to form a relatively brittle structure that can withstand very little mechanical stress and strain. However, through the modification of ELPs to incorporate cystine (S-S) bonds, the scaffold becomes much stronger and able to withstand mechanical stress and strain. The porous structure of the hydrogel also allowed for the delivery of important biomolecules that can be used to maintain stem cell and chondrocyte populations; the authors use this fact to support the use of ELP hydrogel scaffolds in osteogenesis.

Saxena, R; Nanjan, MJ (12 November 2013). "Elastin-like polypeptides and their applications in anticancer drug delivery systems: a review". Drug Delivery. 22 (2): 156–167. doi:http://dx.doi.org/10.3109/10717544.2013.853210. Retrieved 13 April 2017.

Unlike the other articles mentioned, this article discusses the potential of conjugating ELPs to cytotoxic drugs to alter the manner in which the drug is taken up by highly proliferative cancer cells. Through the use of fluorescence imaging, it was shown that the ELP-Doxorubicin complex was taken up to a higher level by the cancer cell when compared to the Doxorubicin alone. Importantly, the ELP protein alone did not exhibit significant cytotoxicity. Although the cytotoxicity of the ELP-Doxorubicin complex and the Doxorubicin alone were comparable, their cell localizations were quite different. The drug by itself has a preference for entering the nucleus of the cell, while the conjugate is absorbed via endocytosis, fuses with the lysosome, and then localizes to the perinuclear membrane following lysosomal action.