Domains 12 to 16 of tropoelastin promote cell attachment and spreading through interactions with glycosaminoglycan and integrins alphaV and alpha5beta1. 266, 308314. 270, 1777817783. *Correspondence: Anthony S. Weiss, tony.weiss@sydney.edu.au, These authors have contributed equally to this work, Fibrous Assemblies: From Synthesis and Nanostructure Characterization to Materials Development and Application, Front. Biol. Human ELN gives rise to a broad variety of splice isoforms, with alternative splicing being observed with exons 22, 23, 24, 26A, 32, and 33 (Fazio et al., 1988; Parks et al., 1992) that result in 13 known human isoforms of the mature tropoelastin protein (Reichheld et al., 2019). Further to this, the flexibility of the hydrophobic domains may also play a key role in self-assembly. This deduction has been corroborated by the observation that tropoelastin with multiple allysine modifications displays conformational sampling comparable to that of the wild-type molecule, suggesting it is more likely to readily participate in self-assembly. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Coacervation is an endothermic, entropically favorable process through which tropoelastin monomers self-assemble into higher order n-mer structures. 82, 335340. J. Biochem. Tropoelastins domains each arise from single exons of the ELN gene. Natl. Targeted disruption of fibulin-4 abolishes elastogenesis and causes perinatal lethality in mice. 26, 17001709. Studies on the reduction of elastin. Natl. (2005). The importance of tropoelastins flexibility during self-assembly has also been examined in the light of natural allysine modifications, which condense to give cross-links within mature elastin (discussed further in the following section) (Ozsvar et al., 2019). 10, 15321541. doi: 10.1007/s004030050227, Tamburro, A. M., Bochicchio, B., and Pepe, A. Tropoelastin: a versatile, bioactive assembly module. The computational model uncovered the contributions of each molecular region to the flexibility of the molecule. Parameter, Testing, and Method. Free energy determinants of secondary structure formation: I. alpha-Helices. Exp. Stages of hierarchical assembly of elastic fibers. 34, 8190. Elastogenesis occurs during replacement fibrosis in human heart disease and can be accelerated in vitro via tropoelastin treatment. FASEB J. Tropoelastin is the soluble precursor of elastin that is secreted as a 60-70-kDa monomer by elastogenic cells such as fibroblasts, lung alveolar cells, chondrocytes, and vascular SMCs [16]. Tropoelastin is a precursor protein of elastin, and is composed of hydrophilic (lysine, valine and proline) and hydrophobic (glycine, valine and proline) domains. J. Biol. doi: 10.1073/pnas.1111615108, Yeo, G. C., Baldock, C., Wise, S. G., and Weiss, A. S. (2017). Adv. Tropoelastin is encoded by the ELN gene, which is present in all vertebrates except jawless fish (Chung et al., 2006). Insights into the structure and behavior of tropoelastin have translated into increasingly sophisticated . Invest. [Epub ahead of print]. 7:32. doi: 10.3389/fphar.2016.00032, Schmelzer, C. E. H., Heinz, A., Troilo, H., Lockhart-Cairns, M. P., Jowitt, T. A., Marchand, M. F., et al. J. Tropoelastin is typically used as a thin coating on tissue culture surfaces. AT acknowledges support from University of Connecticuts Institute for Collaboration on Health, Intervention, and Policy Faculty Research Seed Grant. Acta 303, 363369. Allergan plc (NYSE: AGN), headquartered in Dublin, Ireland, is a bold, global biopharmaceutical company. The ELN gene provides instructions for making a protein called tropoelastin. J. 26, 115124. Elastin makes up the majority of elastic fibers and is formed by the hierarchical assembly of its monomer, tropoelastin. J. Biochem. Trends towards maximal association are apparent when each of these parameters is varied. doi: 10.1016/j.matbio.2006.08.258, Clarke, A. W., Arnspang, E. C., Mithieux, S. M., Korkmaz, E., Braet, F., and Weiss, A. S. (2006). eLife 6:e26526. Bioeng. Cell Biol. Lyophilized Powder. doi: 10.1021/acs.biomac.0c00546, Bochicchio, B., Floquet, N., Pepe, A., Alix, A. J., and Tamburro, A. M. (2004). (2019). doi: 10.1006/jmbi.1995.0502, Yeo, G. C., Baldock, C., Tuukkanen, A., Roessle, M., Dyksterhuis, L. B., Wise, S. G., et al. Chem. 150, 154162. doi: 10.1016/s0021-9258(19)83613-x, Miao, M., Bellingham, C. M., Stahl, R. J., Sitarz, E. E., Lane, C. J., and Keeley, F. W. (2003). The amino acid sequence of domain 36 is unique; furthermore, its sequence confers a positively charged C-terminus comprising lysines between positively charged arginines, forming a RKRK sequence (Vrhovski et al., 1997). doi: 10.1083/jcb.126.2.563, Hu, Q., Reymond, J. L., Pinel, N., Zabot, M. T., and Urban, Z. 4, 508524. The next stage of elastin assembly involves the deposition of tropoelastin spherules onto the microfibril scaffold of elastic fibers. doi: 10.1021/acs.biomac.6b01759, Mackay, J. P., Muiznieks, L. D., Toonkool, P., and Weiss, A. S. (2005). doi: 10.1073/pnas.84.16.5680, Jensen, S. A., Vrhovski, B., and Weiss, A. S. (2000). Sci. Domains 17-27 of tropoelastin contain key regions of contact for coacervation and contain an unusual turn-containing crosslinking domain. Crucially, these simulations revealed that self-assembly starts with a nucleation event and elongation proceeds via both globular and fibrillar structures (Tarakanova et al., 2019a). Characterization of the complete human elastin gene. For example, their inclusion in peptides derived from hydrophobic domains confers decreased times taken for self-assembly, most likely due to their favorable interaction with aqueous solvent (Miao et al., 2003). doi: 10.1046/j.1432-1327.1999.00891.x, Yamauchi, Y., Tsuruga, E., Nakashima, K., Sawa, Y., and Ishikawa, H. (2010). Arch. The elastin receptor complex transduces signals through the catalytic activity of its Neu-1 subunit. J. Struct. Trifluoroethanol may form a solvent matrix for assisted hydrophobic interactions between peptide side chains. Genet. doi: 10.1074/jbc.M104985200, Toonkool, P., Jensen, S. A., Maxwell, A. L., and Weiss, A. S. (2001). Elastin synthesis during perinatal lung development in the rat. (1989). Elastin is the major component of elastic fibers, which are a major component of the tissue that supports the body's joints . Eng. Matrix Biol. Tropoelastins primary sequence is low in complexity and contains repetitive motifs. Biopolymers 107:e23007. J. Mol. doi: 10.1074/jbc.M510833200, Lee, P., Bax, D. V., Bilek, M. M., and Weiss, A. S. (2014). Transglutaminase-mediated cross-linking of tropoelastin to fibrillin stabilises the elastin precursor prior to elastic fibre assembly. Integrins canonically bind proteins containing Arg-Glu-Asp motifs, but this sequence is not found in tropoelastin (Lee et al., 2014). Fazio, M. J., Olsen, D. R., Kuivaniemi, H., Chu, M. L., Davidson, J. M., Rosenbloom, J., et al. Modeling has been verified using wet-bench methodologies, forming a robust suite of complementary methodologies that will undoubtedly become more prevalent for exploring the assembly of biological fibers over time. Elastic fiber formation: a dynamic view of extracellular matrix assembly using timer reporters. It's a stretchy protein that resembles a rubber band it can stretch out (extend) and shrink back (recoil). Domain 36 of tropoelastin in elastic fiber formation. Simul. Eng. We are making enrolling in text alerts easier than ever. doi: 10.1007/s10973-014-4254-9, Debelle, L., and Tamburro, A. M. (1999). For more information, visit Allergans website atwww.Allergan.com. Natl. Evidence for the presence of alpha-aminoadipic acid delta-semialdehyde and its aldol condensation product. doi: 10.1172/jci115204, Sherratt, M., Wess, T. J., Baldock, C., Ashworth, J., Purslow, P., Shuttleworth, C., et al. doi: 10.1161/circimaging.117.007303, Prhashanna, A., Taylor, P. A., Qin, J., Kiick, K. L., and Jayaraman, A. These interactions trigger a wide range of processes including wound healing, elastogenesis and maintenance of stemness (Yeo and Weiss, 2019). 68, 411419. J. Clin. Interestingly, the location and orientation of different domains that contacted each other during self-assembly was noted to be heterogeneous, resulting in head-to-head, tail-to-tail, head-to-tail, and lateral interactions (Tarakanova et al., 2019a). Form. Future investigations will allow the bridging of the gap between mesoscale simulations and microscopically observed coacervation (Clarke et al., 2006). By probing mutations in computational studies that resolve the atomistic structure of the molecule, the deduction of mechanisms associated with changes to functional roles of specific domains has become feasible, and a connection between local structures and biological performance can be established (Figure 2; Tarakanova et al., 2018). doi: 10.1093/protein/13.11.739, Roberts, S., Dzuricky, M., and Chilkoti, A. Calorim. The cross-linking domains are enriched for either Lys-Pro (KP) or Lys-Ala (KA) motifs and form cross-links that link growing tropoelastin chains during elastogenesis; note that exon 6 encodes a KA domain. Biophys. Matrix Biol. (2017). doi: 10.1016/j.jsb.2005.02.005, Martin, S. L., Vrhovski, B., and Weiss, A. S. (1995). Tropoelastin: a novel marker for plaque progression and instability. With this approach, Allergan has built one of the broadest development pipelines in the pharmaceutical industry. The hydrophobic domains contain aliphatic amino acids with proline variations that provide flexibility and the ability to assemble into higher order structures. In addition to its involvement in molecular elasticity, the flexibility of tropoelastin also a key requirement for self-assembly into elastin, with mutations that perturb this having detrimental effects on tissue (Yeo et al., 2016, 2017). Am. 432, 57365751. The coacervate is made insoluble by irreversible crosslinking. Unlike other companies that use paid endorsements and questionable data, NULASTIN science is proven by 3rd party clinical evaluation. 126, 283290. doi: 10.1016/j.actbio.2013.08.003, Wu, W. J., and Weiss, A. S. (1999). Engineering a highly elastic human protein-based sealant for surgical applications. doi: 10.1128/mcb.26.5.1700-1709.2006, Mecham, R. P. (1991). KP domains are found closer toward the N-terminus, whereas KA domains are closer to the C-terminus and include alanine tracts (Indik et al., 1987). (2007). The elastin receptor complex: a unique matricellular receptor with high anti-tumoral potential. Elastogenesis is the term that collectively describes the hierarchical process of elastic fiber formation, and is comprised of distinct phases: tropoelastin synthesis, coacervation, cross-linking, and deposition. 13, 739743. into 200 nm then 12 m spherules, which eventually grow and stabilize into spherules 26 m in diameter (Clarke et al., 2006; Kozel et al., 2006; Tu and Weiss, 2010; Tu et al., 2010). The hydrophobic domains vary in length, with the majority of the shorter (95 residues) domains occurring near the N-terminus, while the longer (up to 55 residues) domains are found within tropoelastins central and C-terminal regions (Indik et al., 1989). Single nucleotide polymorphisms and domain/splice variants modulate assembly and elastomeric properties of human elastin. Biochimie 86, 173178. Bull. The study is designed to evaluate the efficacy of two formulations of a cross-linked tropoelastin matrix given the product codes ELAPR002f (collectively referred to as ELAPR or ELAPR002) for the treatment of rolling atrophic acne scars when administered as intradermal implants. Founder, Elastagen Pty Ltd (sold to Allergan/AbbVie . (2005). After a period of collaboration with the Elastagen team, US biopharmaceutical giant Allergan acquired Elastagen in 2018 for over $350 million in total deal value. Initially, in vitro coacervation is characterized by the rapid aggregation of tropoelastin. J. Elastins subunit, tropoelastin, is a soluble 6070 kDa protein which has been intensely studied over the past three decades. Furthermore, tropoelastins hydrophobic and cross-linking domains are arranged in alternating patterns throughout the majority of the molecule, giving rise to both inter- and intra-domain level repetition. Tropoelastin is secreted as a 6070 kDa protein to the cell surface where it participates in self-assembly (Hinek and Rabinovitch, 1994; Figure 3). 289, 1005710068. doi: 10.1016/j.matbio.2009.10.003, Tu, Y., Wise, S. G., and Weiss, A. S. (2010). Isolation and characterization of crosslinked peptides from elastin. (1995). They can be categorized as either hydrophobic or cross-linking based on their functionality and amino acid content (Figure 1). Interactions of fibrillin-1 with heparin/heparan sulfate, implications for microfibrillar assembly. Modulative effects are also observed within full length tropoelastin, where disruptions to domain 26 diminish self-assembly (Jensen et al., 2000), highlighting the context of primary sequence on higher order structures. Codistribution analysis of elastin and related fibrillar proteins in early vertebrate development. . With commercial operations in approximately 100 countries, Allergan is committed to working with physicians, healthcare providers and patients to deliver innovative and meaningful treatments that help people around the world live longer, healthier lives every day. J. Biol. Biol. Assembly proceeds from a nucleation event and undergoes elongation in a step-wise manner to form a multimer which can occur in a head-to-tail fashion (Wise et al., 2014). The most commonly investigated isoform contains domain 26A and lacks domain 22, and is predominantly found in elastic tissues (Indik et al., 1987; Vrhovski et al., 1997). Binding of EDPs to the ERC induces a number of biological effects including migration, adhesion, proliferation, protease expression, and secretion. Direct observation of structure and dynamics during phase separation of an elastomeric protein. The self-assembly properties and nanostructure of these extra teleost isoforms are yet to be investigated. Am. Cell Res. The prevention of early self-aggregation in vitro is thought to be mediated by chaperone proteins (Hinek and Rabinovitch, 1994; Miao et al., 2013). 15, 786801. U.S.A. 116, 20422051. (1988). doi: 10.1016/j.bbrc.2010.05.013, Elvin, C. M., Carr, A. G., Huson, M. G., Maxwell, J. M., Pearson, R. D., Vuocolo, T., et al. J. Biol. Natl. Eur. J. Hum. Acta 761, 1722. Transient tropoelastin nanoparticles are early-stage intermediates in the coacervation of human tropoelastin whose aggregation is facilitated by heparan sulfate and heparin decasaccharides. Biopolymers 20, 12471260. Injectable biomaterial compositions formed from tropoelastin for tissue repair and restoration. Biol. Acad. We are very interested in the blend of biochemistry and cell biology, as well as the tissue engineering and regenerative medicine opportunities provided by this amazing elastic protein. Increased cyclic GMP levels lead to a stimulation of elastin production in ligament fibroblasts that is reversed by cyclic AMP. The advantage of coarse-grained methodologies is that they allow for the simulation of timescales of large molecular systems on the order of microseconds, which are otherwise computationally infeasible with classical full-atomistic molecular dynamics. Insights into the structure and dynamics of lysyl oxidase propeptide, a flexible protein with numerous partners. Annabi, N., Zhang, Y. N., Assmann, A., Sani, E. S., Cheng, G., Lassaletta, A. D., et al. Chem. Nature 246, 461466. Attempts to characterize tropoelastins structure have seen a gradual shift from the belief that tropoelastins domains have fixed structures, to understanding that the majority of its domains are capable of transitioning between random coils and transient ordered structures. (1973). (2017). Isolation and characterization of human elastin cDNAs, and age-associated variation in elastin gene expression in cultured skin fibroblasts. Front. (2018). Biopolymers 29, 16991706. Synthesis and properties of crosslinked recombinant pro-resilin. 38, 280291. Elastagen's revolutionary recombinant human tropoelastin, is identical to that present in human tissue and has many clinical applications, including effective breakthrough treatments for acne scars, stretch marks, aesthetic skin repair and wound repair. Computational approaches have gained popularity in recent decades as their methodologies have been refined to provide accurate atomistic scale insights into molecular structure and movement (Tarakanova et al., 2018). Tropoelastin is a flexible molecule that retains its canonical shape. Reichheld, S. E., Muiznieks, L. D., Huynh, Q., Wang, N., Ing, C., Miao, M., et al. doi: 10.1002/ajmg.1320340115, Indik, Z., Yeh, H., Ornstein-Goldstein, N., Sheppard, P., Anderson, N., Rosenbloom, J. C., et al. Proline-poor hydrophobic domains modulate the assembly and material properties of polymeric elastin. Tropoelastins hydrophobic domains are predominantly responsible for the random coil content of the monomer, and are the result of the unique pairing of proline and glycine pairs that are interspersed throughout the majority of hydrophobic domains (Rauscher and Pomes, 2017). The isoform-function theory is further reinforced by the presence of two different ELN genes within teleosts that are differentially expressed both spatially and temporally during development (Miao et al., 2007). Chem. Proc. Matrix Biol. doi: 10.1016/s0003-9861(02)00719-1, Muiznieks, L. D., Reichheld, S. E., Sitarz, E. E., Miao, M., and Keeley, F. W. (2015). Targeted modulation of tropoelastin structure and assembly. ACS Biomater. Biochemistry 37, 1461314622. Banded fibers in tropoelastin coacervates at physiological temperatures. Sci. The elasticity of organs and tissues in vertebrates is due to the presence of elastin, and an insoluble protein whose soluble monomer, tropoelastin, is enzymatically cross-linked through -amino groups of lysine residues. (2020). Biochemistry of tropoelastin. 31, 261272. doi: 10.1073/pnas.1014280108. Nat. Natl. Elastagen Pty Ltd, a clinical stage company developing medical device products based on recombinant tropoelastin, today announced. doi: 10.1038/246461a0, Haust, M. D., More, R. H., Bencosme, S. A., and Balis, J. U. Biotechnol. Int. A., Rongish, B. J., Czirok, A., Zach, J., Little, C. D., Davis, E. C., et al. Allergan is an industry leader in Open Science,a model of research and development, which defines our approach to identifying and developing game-changing ideas and innovation for better patient care. II. Tropoelastin is a low complexity protein on both primary and secondary sequence levels. Med. Variations in the relative abundance of alternatively spliced ELN mRNA transcripts have been observed between tissues, and this diversity is thought to be necessary for the fine tuning of the mechanical characteristics of tissues to suit their unique functional requirements (Reichheld et al., 2019). Tropoelastin is a unique protein with biochemical and physical properties that allow it to rapidly self-assemble into fibrous structures. Matrix Biol. J. Biol. doi: 10.1016/j.matbio.2019.06.010, Reichheld, S. E., Muiznieks, L. D., Stahl, R., Simonetti, K., Sharpe, S., and Keeley, F. W. (2014). Macromol. FEBS J. J. Biol. Res. Cell. (1989). Molecular dynamics modeling of aggregating tropoelastin-derived peptide chains points to the maintenance of a hydrated, disordered, liquid-like state due to the formation of short-lived inter-chain bonds (Rauscher and Pomes, 2017; Reichheld et al., 2020), mostly likely due to the inducement of random coils by PG repeats (vide supra). doi: 10.1371/journal.pone.0046130, Hedtke, T., Schrader, C. U., Heinz, A., Hoehenwarter, W., Brinckmann, J., Groth, T., et al. doi: 10.1016/s0968-4328(99)00082-7, Tajima, S., Wachi, H., Uemura, Y., and Okamoto, K. (1997). doi: 10.1111/febs.14929, Hinderer, S., Shena, N., Ringuette, L. J., Hansmann, J., Reinhardt, D. P., Brucker, S. Y., et al. The hydrophobic domains are involved in coacervation and the hydrophilic domains are used for cross-linking. Tropoelastin was revealed to be an asymmetric molecule with distinct N- and C-terminal regions that are respectively referred to as the head and foot of the molecule. doi: 10.1016/0378-1119(94)00848-m, McLaughlin, P. J., Chen, Q., Horiguchi, M., Starcher, B. C., Stanton, J. Structure of the elastin gene and alternative splicing of elastin mRNA: implications for human disease. Sci. More recently, the computational model of tropoelastin has been leveraged to characterize higher-order structures and probe self-assembly (Tarakanova et al., 2019a). Thermal compaction of disordered and elastin-like polypeptides: a temperature-dependent, sequence-specific coarse-grained simulation model. doi: 10.1016/s0022-5320(83)80021-5, Broekelmann, T. J., Kozel, B. Struct. Coacervation optimally occurs at physiological temperature, however, in vitro coacervation can also occur at lower temperatures depending on experimental conditions and the choice of tropoelastin isoform or derivative (Yeo et al., 2011). Our understanding of key aspects of the assembly process have been unclear due to the intrinsic properties of elastin and tropoelastin that render them difficult to study. The smallest amino acid, glycine is known to promote flexibility within local structures due to lack of steric hindrance, whereas prolines restrictive sidechain inhibits conformational sampling and disrupts the formation of prolonged secondary structures (Roberts et al., 2015). The ability to stretch and recoil arises from the biochemical properties of elastins monomer, tropoelastin (discussed below). Collapse Section. Chem. The narrow specificity to v3 and 53 may also be beneficial compared with other ECM adhesion molecules such as fibronectin (which can adhere to up to 20 types of integrin) which may compete with and modulate binding to tropoelastin, and deliver opposing effects on cell proliferation. Characterization of an unusual tropoelastin with truncated C-terminus in the frog. Dissection of human tropoelastin: exon-by-exon chemical synthesis and related conformational studies. Sci. doi: 10.1021/bi060289i, Tarakanova, A., and Buehler, M. J. doi: 10.1074/jbc.M004265200, Kadler, K. E. (2017). Adv. 10:034102. doi: 10.1088/1748-6041/10/3/034102, Hinek, A., Keeley, F. W., and Callahan, J. Similarly, a mutation model associated with cutis laxa, or loose skin disease (Hu et al., 2006), was found to exhibit higher stability compared with the wild-type molecule due to the increased longevity of its salt bridges (Hu et al., 2006; Tarakanova et al., 2018). Shape of tropoelastin, the highly extensible protein that controls human tissue elasticity. Biomacromolecules 21, 35233538. Pathol. Mater. Pepe, A., Flamia, R., Guerra, D., Quaglino, D., Bochicchio, B., Pasquali Ronchetti, I., et al. J. Biol. Acad. The lysines of domain 15 and 17 are believed to play key roles in this interaction. Acta Biomater. J. Biochem. Today Biol. (2007). Structural analysis of photocrosslinkable methacryloyl-modified protein derivatives. 264, 88878891. doi: 10.1016/j.biochi.2004.03.002, Sandberg, L. B., Gray, W. R., Foster, J. Biophys. doi: 10.1126/sciadv.1501145, Yeo, G. C., and Weiss, A. S. (2019). Biochemistry 52, 77317741. Further down the molecule, the cell-interactive C-terminus was noted to be highly flexible, indicating that high conformational sampling could be conducive to tropoelastins interactions between cell-surface receptors and elastic fiber-associated proteins. doi: 10.1248/bpb.b13-00933, Ozsvar, J., Tarakanova, A., Wang, R., Buehler, M. J., and Weiss, A. S. (2019). Elastagen's revolutionary recombinant human tropoelastin, is identical to that present in human tissue and has many clinical applications, including effective breakthrough treatments for acne. J. Med. The business could generate net sales of approximately $7 to $8 billion in 2025 from $3.8 billion in 2017. Elastin as a random-network elastomer: a mechanical and optical analysis of single elastin fibers.
