Natural resilin

Amino acid analysis, by reverse-phase HPLC, of acid-hydrolyzed uncross-linked recombinant resilin and cross-linked recombinant resilin clearly shows the presence of dityrosine in the cross-linked sample (Figure 9.3c). Further evidence of the presence of dityrosine was obtained by UV irradiation (Xmax,ex 315 nm Xmax,em 409 nm). Dityrosine endows natural resilin with pH-dependent blue fluorescence [38] on UV irradiation. The cross-linked recombinant resilin material was similarly fluorescent, strongly suggesting dityrosine cross-links. 

No results have been acquired to date on the fatigue lifetime of recombinant resilin however, it is informative to consider the performance of natural resilin. 

To further understand and manipulate the fiinctional and structural properties of natural resilin, Qin et al expressed the three exons of the Drosophila CG15920 gene, which encodes the full-length native resilin sequence, including the chitin-binding domain. This recombinant resilin exhibits comparable structural and mechanical behaviors to those previously reported, and the introduction of chitin-binding domain provides additional opportunities for formation of the resilin-chitin cuticle composite structure. 

Intrigued by the excellent mechanical properties and hydro-philicity of natural resilin, and facilitated by recent expression... 

FIGURE 9.3 Cross-linked recombinant resilin. (a) Structure of the dityrosine adduct, (b) A cross-linked moulded rod. (c) HPLC analysis of acid-hydrolyzed uncross-Unked recombinant resilin and cross-linked recombinant resilin. (From Elvin, C.M., Carr, A.G., Huson, M.G., Maxwell, J.M., Pearson, R.D., Vuocolo 1, T., Liyon, N.E., Wong, D.C.C., Merritt, D.J., and Dixon, N.E., Nature, 437, 999, 2005.)... 

Other clues to the self-association of recombinant resilin in solution, and thus a degree of defined stmcture, include the propensity of the monomer proteins to covalently cross-link very rapidly through dityrosine side chains using a mthenium-based photochemical method [29]. Proteins which do not naturally self-associate do not form biomaterials when exposed to the Ru(ll)-based photochemical procedure (Elvin, C.E. and Brownlee, A.G., personal communication). Furthermore, Kodadek and colleagues showed that only intimately associated proteins are cross-linked via this zero-A photochemistry procedure [45]. 

The amino acid composition of resilin was elucidated shortly after its first description and was shown to be unique among other structural proteins found in Nature a summary of the amino acid sequence is given in Table 1. 

Fig. 22 Photo-crosslinked titin-mimetic hydrogel, with the circles indicating the folded immuno-globulin-like domains and the wavy lines indicating the resilin-like domains. Reproduced from [235] with permission from Nature Publishing Group, copyright 2010...

Figure 3 Resilience measurements of cross-linked elastomers chlorobutyl rubber (CNR), polybutadiene rubber (BR), and cross-linked recl-resilin. Reproduced with permission from Elvin, C. M. Carr, A. G. Huson, M. G. etal. Nature 2005,437,999. Copyrighf 2005 Nature Publishing Group.

Figure 4 Force-extension curves of titin-mimetic polypeptides, (a) (G-R)4 and (b) GRG5RG4R (G represents the GB1 domain and R represents the random-coil resilin domain). Reproduced with permission from Lv, S. Dudek, D. M. Cao, Y. etal. Nature 20 0, 465,69." Copyright 2010 Nature Publishing Group.

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