Editorial Cite This: Biomacromolecules 2017, 18, 3469-3470
pubs.acs.org/Biomac
Organized Peptidic Nanostructures as Functional Materials
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naphthalene diimide (NDI)-appended peptide amphiphile (Das et al. DOI: 10.1021/acs.biomac.7b01048) was designed for the formation of hydrogels based on a combination of hydrogen bonding and hydrophobic effects. The NDI group not only helps the self-assembly but also introduces optical functionality for imaging and sensing. An amazing example of peptide−inorganic hybrid materials is the finding of biomimetic underwater adhesives formed by a strong multivalent electrostatic combination between cationic peptides and polyoxometalates (Li et al. DOI: 10.1021/acs.biomac.7b00817). Peptidebased adhesives with strong shear strength can serve as medical glue for clinical treatment. A biomimetic dipeptide-carbon nitride hydrogel (Park et al., DOI: 10.1021/acs.biomac. 7b00889), capable of light harvesting and photosynthesis, was constructed by controlling noncovalent interactions between both dipeptide and carbon nitride. These research studies demonstrate the versatility of peptide−inorganic coassembly as a fabrication strategy. The intermolecular interactions mainly determine the thermodynamics of peptide self-assembly, that is to say, the energy contribution to the nanostructures (such as nanospheres, nanofibers, nanotubes, etc.) eventually formed. However, the environmental conditions (such as pH, temperature, and ionic strength) subjected to peptide building blocks will also influence the assembly kinetics, which can vary the thermodynamics of assembled nanostructures. In this special issue, Adams et al. (DOI: 10.1021/acs.biomac.7b00823) investigated the structural evolution of fibrous peptide hydrogels due to drying by small-angle neutron scattering (SANS), determining the effect of water on the primary fiber in the process of drying. Super-resolution fluorescence microscopy (e.g., STORM) was used to inspect dynamic processes of self-assembly of peptide fibrils (Lu et al., DOI: 10.1021/acs. biomac.7b00465). Multicolor STORM imaging allows for probing monomer exchange dynamics in real time showing assembly and disassembly of fibrils. This technique offers the possibility of studying the kinetics of peptide self-assembly by varying the environmental conditions. The molecular structure of peptide building blocks directly correlates with the thermodynamics of self-assembly, thus leading to control of assembled nanostructures and properties. For example, the length of the conjugated hydrocarbon plays a critical role in tuning the conformation of assembled nanofibers (Cui et al. DOI: 10.1021/acs.biomac.7b00992). It was found that the longer ones promote β-sheet formation and the short ones stabilize α-helices to some extent. Self-assembly of peptide monolayers on gold nanoparticles leads to a defined change in peptide conformation from random coil to coiled-coil structures, enabling enhancement of the catalytic activity (Koksch et al. DOI: 10.1021/acs.biomac.7b00887). Precise control of surface wettability of microfluidic devices allows for
n Nature, life function and activity substantially depend on self-assembly and self-organization of biomolecular building blocks. Among a variety of biomolecules, peptides consisting of amino acids have become most popular and promising over decades for development of functional materials owing to the ease of availability, programmable molecular motif, good biocompatibility and biodegradation, versatile functionality, and low cost effectiveness.1−4 Peptide self-assembly, as a fabrication technique, has been a burgeoning field, and new materials created by this technique provide opportunities for advancing nanotechnology, bioenergy, and nanomedicine. Although there is still much work and brain power needed to understand the structure formation of peptide assemblies because of the system complexity and interplay between thermodynamics and kinetics, one has to consider the next goals to achieve desired functions. Therefore, it is timely to publish a special issue on the topic of “Organized Peptidic Nanostructures as Functional Materials”, covering the latest exciting findings and advances on peptide−polymer, peptide− pigment, and peptide−inorganic hybrid materials, responsive materials, and multifunctional materials based on peptide and peptide-modulated self-assembly. Assembled structures and functionalities are tightly related to cooperation and compromise of multiple intermolecular interactions such as hydrophobic effects, hydrogen bonds, and electrostatic forces. How to rationally control these weak noncovalent interactions will be crucial for achieving precise structural organization and functional optimization. All contributors more or less pay attention to the design of intermolecular interactions between peptides or between peptides and another component such as polymer, pigment, and inorganics, as this is the key point in controlling organized nanostructures and corresponding functions. For example, a review article (Meier et al., DOI: 10.1021/acs.biomac.7b00764) in this special issue illustrates the increasing importance of peptide-based hybrid materials with emphasis on peptide− polymer ones toward biomimetic fabrication and biomedical applications. The intermolecular interactions driving the selfassembly of nanostructures can be controlled on the molecular level through polymer chemistry, thus precisely tuning the obtained nanostructures, such as micelles, vesicles, tubes, and fibers. Stimuli responsiveness due to introduction of polymer components can also be expected, which is highly appreciated for controlled and targeted drug delivery. The flexible variation of peptide sequences and polymer blocks may fulfill a variety of functions, thus extending the versatility of peptide-based materials. Such subtle cooperative self-organization has been demonstrated in creation of biomimetic photosystems and therapeutic nanoagents, e.g., peptide−porphyrin coassembly.5,6 In this special issue, Li et al. (DOI: 10.1021/acs.biomac. 7b00780) expanded the pigment to a donor−acceptor pair, both of which were entrapped within the assembled dipeptide nanoparticles. The resulting nanoparticles can yield singlet oxygen for killing cancer cells based on energy transfer by twophoton-activated photodynamic therapy. In addition, a © 2017 American Chemical Society
Special Issue: Organized Peptidic Nanostructures as Functional Materials Published: November 13, 2017 3469
DOI: 10.1021/acs.biomac.7b01437 Biomacromolecules 2017, 18, 3469−3470
Biomacromolecules
Editorial
and advanced applications. We are delighted to have made this special issue a reality, and we are very grateful to our contributors for their passion, commitment, and skill. Overall, we hope that this special issue will provide clues for readers, helping in the future development of this field, and we also expect bigger breakthroughs in hitherto unexplored areas of science.
drop-by-drop formation of multiple emulsions with hierarchical encapsulation of peptides or proteins, presenting a potent strategy for controlled preparation of biomolecular drug formulations (Knowles et al. DOI: 10.1021/acs.biomac. 7b01159). Amphiphilic 3- and 4-helix peptide−polyethylene glycol (PEG)−lipid hybrid conjugates can cooperatively selfassemble into nanophase-separated sub-20 nm stable micelles with precise control over the local multivalent state of ligands on the micelle surface (Xu et al., DOI: 10.1021/acs.biomac. 7b00917). The composite micelles are rather stable in the presence of serum albumin, presenting potential for application in drug delivery. In another contribution, Lee et al. (DOI: 10. 1021/acs.biomac.7b00951) showed that rational design of chemical structures of antibacterial peptides and precise control of their interactions can lead to the formation of various nanostructures such as micelles, fibrils, vesicles, sheets, and planar networks, which were found to have diverse antimicrobial and anticancer activities. A most promising perspective on the organized peptidic nanostructures as functional materials is expected in the research area of biomedical applications, heavily focusing on drug delivery, tumor therapy, and tissue engineering. In this special issue, a significant amount of research has focused on peptide-based hydrogels with integration of a variety of functions toward biomedical applications. For example, the assembled fibrous hydrogels were unraveled to be effective in triggering antitumor immune response without addition of antigens, immune regulatory factors, and adjuvants (Yan et al., DOI: 10.1021/acs.biomac.7b00787). The innate immune response at the tumor site is activated due to the presence of helical peptide nanofibers, resulting in efficient suppression of tumor growth. Arginine-presenting peptide hybrid hydrogels with attachment of hydroxyapatite were developed by cooperative self-assembly (Adler-Abramovich et al. DOI: 10. 1021/acs.biomac.7b00876). They were demonstrated to have high mechanical strength and capable of supporting cell adhesion, proliferation, and growth, suggesting the potential for improved bone regeneration. Thermoresponsive fibrous hydrogels were obtained by self-assembly of peptide amphiphiles with a long fatty acyl chain and exhibited potential antimicrobial activity against both Gram-positive and -negative bacteria (Banerjee et al. DOI: 10.1021/acs.biomac.7b01006). How to precisely release payloads in response to delivery sites of interest has been a great challenge for a long time, and viruslike nanoparticles with controlled size enable new chances (van Hest et al. DOI: 10.1021/acs.biomac.7b00640). Responsive release in the tumor environment can be achieved by introducing responsive groups into the peptide sequences. For example, assembled fibrous hydrogels formed from short peptides (Ac-I3SLKG-NH2) can be sensitive to overexpressed proteinase MMP-2 in tumors (Xu et al., DOI: 10.1021/acs. biomac.7b00911), and peptide-dendrimeric nanogels can be responsive to a redox ambient in tumors (Xu and Gu et al. DOI: 10.1021/acs.biomac.7b00649). Furthermore, the basic study of hydrogels has moved toward practical applications, e.g., tuning the viscoelasticity by specific molecular recognition (Nilsson et al. DOI: 10.1021/acs.biomac.7b00925) or using new building blocks, e.g., cyclic dipeptides as injectable peptide gelators for regenerative medicine (Govindaraju et al. DOI: 10. 1021/acs.biomac.7b00924). This issue should demonstrate that the field of peptide selfassembly has extensively expanded not only toward structure control and regulation but also toward functional integration
Xuehai Yan*,†,‡,§ Helmuth Möhwald*,∥ †
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State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China ‡ Center for Mesoscience, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China § University of Chinese Academy of Sciences, Beijing 100190, China ∥ Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam/Golm, Germany
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Xuehai Yan: 0000-0002-0890-0340 Helmuth Möhwald: 0000-0001-7833-3786 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
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REFERENCES
(1) Adler-Abramovich, L.; Gazit, E. The Physical Properties of Supramolecular Peptide Assemblies: From Building Block Association to Technological Applications. Chem. Soc. Rev. 2014, 43, 6881−6893. (2) Wang, J.; Liu, K.; Xing, R.; Yan, X. Peptide Self-assembly: Thermodynamics and Kinetics. Chem. Soc. Rev. 2016, 45, 5589−5604. (3) Ulijn, R. V.; Woolfson, D. N. Peptide and protein based materials in 2010: from design and structure to function and application. Chem. Soc. Rev. 2010, 39, 3349−3350. (4) Cui, H.; Webber, M. J.; Stupp, S. I. Self-Assembly of Peptide Amphiphiles: From Molecules to Nanostructures to Biomaterials. Biopolymers 2010, 94, 1−18. (5) Liu, K.; Xing, R. R.; Li, Y. X.; Zou, Q. L.; Möhwald, H.; Yan, X. H. Mimicking Primitive Photobacteria: Sustainable Hydrogen Evolution Based on Peptide-Porphyrin Co-Assemblies with SelfMineralized Reaction Center. Angew. Chem., Int. Ed. 2016, 55, 12503− 12507. (6) Zou, Q. L.; Abbas, M.; Zhao, L. Y.; Li, S. K.; Shen, G. Z.; Yan, X. H. Biological Photothermal Nanodots Based on Self-assembly of Peptide-Porphyrin Conjugates for Antitumor Therapy. J. Am. Chem. Soc. 2017, 139, 1921−1927.
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DOI: 10.1021/acs.biomac.7b01437 Biomacromolecules 2017, 18, 3469−3470
