Protein-based nanostructure Marlon D. Jerez November 7, 2017
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Intr Introdu oduct ctio ion: n: Defin Definit itio ion n
The complexity and sophistication of protein-based structures and materials in nature hints to the great great potentia potentiall of design designed ed protein protein-ba -based sed materials materials and nanostru nanostructu ctures. res. Amino Amino acid sequen sequences ces encode encode the comple complex x structur structures es and function functionss of protein proteins, s, thus, thus, the manipu manipulat lation ion of protein protein sequenc sequencee can generate generate structur structural al and functio functional nal buildi building ng blocks, blocks, and encode encode the formation of supramolecular protein assemblies. Therefore, if it possible to manipulate protein structure and function, it would be possible to generate sophisticated nanotools. In this sense, the application of protein to assemble new nanostructures has been recently explored. Self-assembling and nanostructure patterning based on different biomolecules have been widely explored recently, being most of the works based on the assembly of nucleic acids. DNA provides provides a good control control over the assembly assembly.. Howeve However, r, DNA cannot provide the functional functional and structural diversity of proteins. One of the main limitations for rational protein design is the lack of a deep understanding about how protein sequence-structure-function relate. The three dimensional structure of proteins is defined by their primary sequence and is directly related to its function. Thus,manipulation of the protein structure through changes in its primary sequence can generate different nanostructure tructuress and functional functionaliti ities. es. Most Most of the nanostr nanostructu uctures res are based based on a particu particular lar type of proteins, which are the repeat proteins. Due to their modular nature, these proteins are better suited to be used as building blocks than other protein scaffolds [7]. Repeat proteins are non-globular structures that are involved in essential cellular processes acting acting typic typicall ally y as scaffol scaffolds ds for the mediat mediation ion of protein protein–pro –protei tein n intera interactio ctions ns [1]. [1]. There There are a variety of repeat protein families composed of units with different structures, being alpha helica helical, l, beta-stra beta-strand nd or a mixture mixture of the two secondary secondary structure structure element elements. s. Some of the most abundant and well studied classes of repeat proteins are formed by the repetition of simple 1
building blocks, such as; tetratricopeptide repeats (TPR), ankyrin repeats (ANK), leucine rich repeats (LRR), armadillo repeats (ARM), and transcription activator-like (TALE) [3].
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Structures and applications
Considering the main features of repeat proteins previously described, it is evident that they are ideally suited for nanobioengineering. Each repeat unit can be used as a building block with individually engineered properties (stability, function, and interactions between modules) in order to generate designed proteins and higher order assemblies. Because repeat proteins are simplified systems, it is possible to control how protein sequence-structure-function relate in these type of proteins [4]. The tetratricopeptide repeat (TPR) is an example of the wide range of possibilities that repeat proteins give to the field of protein assemblies. TPR consists of 34 amino acid sequence that folds in helix-turn-helix motif [2]. To create new TPR proteins that capture the sequencestructure relationship of the TPR fold, a consensus TPR (CTPR) sequence was designed by the Regan Laboratory from the statistical analysis of natural TPRs. The modular structure of the CTPR repeat proteins and the basic understanding of their sequence-structure relationships opens the possibility to modulate the interaction between the units. Thus, it is possible the formation of different protein assemblies in a controlled manner through a hierarchical self-assembly including nanofibers, nanotubes, and nano-structured thin films.
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Nanofibers
Protein nanofibers are generated using the intrinsic head-to-tail interactions and a simple disulfide bond staple to fix those interactions between molecules. By combining the head-to-tail interactions observed in the CTPR crystals with the introduction of specific reactives into the CTPR units, linear higher order structures have been assembled [6].
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Nanotubes
CTPR protein nanotubes formed by the introduction of a second interacting interface that provides an extra dimension to the final structure by allowing two superhelical CTPR molecules to assemble [5].
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Nano-structured thin films
One advantage of using CTPR proteins for the generation of highly ordered materials and devices is the fact that these proteins can maintain their structure in the solid state. Nanostructured protein thin films are generated using the intrinsic head-to-tail and side-to-side assembly properties of CTPRs through specific noncovalent interaction
References [1] Andrade, M. A., Perez-Iratxeta, C., and Ponting, C. P. Protein repeats: Structures, functions, and evolution. Journal of Structural Biology 134 , 2 (2001), 117 – 131. [2] D’Andrea, L. D., and Regan, L. Tpr proteins: the versatile helix. Trends in Biochemical Sciences 28 , 12 (2003), 655 – 662.
[3] Fuchs, S., and Coester, C. Protein-based nanoparticles as a drug delivery system: chances, risks, perspectives. Journal of Drug Delivery Science and Technology 20 , 5 (2010), 331 – 342. [4] Mejias, S. H., Aires, A., Couleaud, P., and Cortajarena, A. L. Designed Repeat Proteins as Building Blocks for Nanofabrication . Springer International Publishing, Cham,
2016, pp. 61–81. [5] Mejias, S. H., Couleaud, P., Casado, S., Granados, D., Garcia, M. A., Abad, J. M., and Cortajarena, A. L. Assembly of designed protein scaffolds into monolayers
for nanoparticle patterning. Colloids and Surfaces B: Biointerfaces 141, Supplement C (2016), 93 – 101. [6] Mejias, S. H., Sot, B., Guantes, R., and Cortajarena, A. L. Controlled nanometric fibers of self-assembled designed protein scaffolds. Nanoscale 6 (2014), 10982–10988. [7] Tarhini, M., Greige-Gerges, H., and Elaissari, A. Protein-based nanoparticles: From preparation to encapsulation of active molecules. International Journal of Pharmaceutics 522 , 1 (2017), 172 – 197.
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