Periodic Reporting for period 1 - SQSig (Oligo-Squaramide Rigid-Rods for Artificial Transmembrane Signaling)
Reporting period: 2020-09-01 to 2022-08-31
Conformational change relayed over several nanometers is central to the function of many proteins. For example, G-protein coupled receptors (GPCRs) are transmembrane proteins that are used by cells to transmit information through their membranes and are responsible for some of the most important biological functions, such as sight and taste. Many GPCRs bind a ligand to their extracellular region, which provokes a conformational change and initiates a biological process inside the cell. The number of existing synthetic systems able to transfer conformational information across several nanometres is scarce. Exploring new designs can lead to applications in a wide range of contexts.
Replicating allosteric regulation mechanisms could allow researchers to bypass endogenous signaling pathways in cells, a key target in medicinal chemistry, and will provide important communication tools for the development of molecular robots and fully synthetic cells. Such systems can be the basis of the materials and therapies of the future, and will use artificial communication relays, for example, to share information between different compartments or to interconnect different events within molecular factories. Moreover, a detailed understanding of the self-assembly properties and mode of operation of new molecular systems is crucial for scientific progress.
The main objective of this project was to exploit the self-assembly properties of squaramides (SQs) to create an artificial relay of information. Monomeric SQs form ribbons with all the SQs oriented in the same direction. We designed a scaffolded oligo-SQ array that would form intramolecular hydrogen-bonded ribbons aligned in either one direction or the opposite one. Inverting the directionality of the terminal SQ of the ribbon would initiate a domino effect that would switch the orientation of the whole array. Upon functionalization, binding of an external ligand to the squaramide in one terminus would switch the directionality of the entire SQ-ribbon and provoke a spectroscopic response at the other end of the relay. Thus, this system would represent a synthetic GPCR, able to transmit conformational information across its linear structure, and with the potential to perform artificial signal transduction in bilayer membranes.
Conclusions of the action:
During this project, a multi-SQ hydrogen-bond relay has been arrayed along a rigid rod oligo(phenylene-ethynylene) (OPE) scaffold. The rigid rod dictates the length of the SQ information relay and prevents its folding and structural collapse.
The relay adopts either a parallel or an antiparallel orientation relative to the scaffold; the preferred orientation can be dictated by a director group at one end.
Installing a proton-responsive director in a 2 nm long SQ relay permitted multiple reversible changes in relay orientation in response to protonation/deprotonation signals. Moreover, a chemical fuel also acted as a signal, affording the first example of a molecular communication relay operating under out-of-equilibrium conditions.
Replicating allosteric regulation mechanisms could allow researchers to bypass endogenous signaling pathways in cells, a key target in medicinal chemistry, and will provide important communication tools for the development of molecular robots and fully synthetic cells. Such systems can be the basis of the materials and therapies of the future, and will use artificial communication relays, for example, to share information between different compartments or to interconnect different events within molecular factories. Moreover, a detailed understanding of the self-assembly properties and mode of operation of new molecular systems is crucial for scientific progress.
The main objective of this project was to exploit the self-assembly properties of squaramides (SQs) to create an artificial relay of information. Monomeric SQs form ribbons with all the SQs oriented in the same direction. We designed a scaffolded oligo-SQ array that would form intramolecular hydrogen-bonded ribbons aligned in either one direction or the opposite one. Inverting the directionality of the terminal SQ of the ribbon would initiate a domino effect that would switch the orientation of the whole array. Upon functionalization, binding of an external ligand to the squaramide in one terminus would switch the directionality of the entire SQ-ribbon and provoke a spectroscopic response at the other end of the relay. Thus, this system would represent a synthetic GPCR, able to transmit conformational information across its linear structure, and with the potential to perform artificial signal transduction in bilayer membranes.
Conclusions of the action:
During this project, a multi-SQ hydrogen-bond relay has been arrayed along a rigid rod oligo(phenylene-ethynylene) (OPE) scaffold. The rigid rod dictates the length of the SQ information relay and prevents its folding and structural collapse.
The relay adopts either a parallel or an antiparallel orientation relative to the scaffold; the preferred orientation can be dictated by a director group at one end.
Installing a proton-responsive director in a 2 nm long SQ relay permitted multiple reversible changes in relay orientation in response to protonation/deprotonation signals. Moreover, a chemical fuel also acted as a signal, affording the first example of a molecular communication relay operating under out-of-equilibrium conditions.
To develop our system, we have used oligo-phenylene ethynylenes (OPEs) as rigid rods, functionalized with squaramide (SQ) units. These compounds were prepared using standard synthetic procedures, which were optimized to obtain the best outputs. Mono-, bis- and tris-SQ OPEs were prepared and studied both in solution, by NMR spectroscopy, and in solid state, by single crystal X-ray diffraction. The crystal structures showed a perfect match between the repeat unit distances in the SQ relay and in the OPE.
SQ-OPE relays were prepared with different director groups in one end of their structure. We observed two opposite orientations of the SQ relays with respect to the OPE rigid rod. The orientation and robustness of the relay was dictated by the hydrogen-bonding properties of the director, thus determining the orientation and interaction capability of a remote SQ unit.
We installed a switchable director into a tris-SQ relay of 2 nm length (a distance similar to the thickness of the lipophilic region of a bilayer membrane). The resulting device responded to a simple chemical messenger, the proton, relaying the conformational change caused by protonation of the director to the end of the scaffold. Addition of a second messenger, a base, caused the recovery of the initial conformational state, which was able to accept subsequent protonation/deprotonation cycles.
The reversible communication device described above was then combined with a chemical fuel to produce an out-of-equilibrium system. The chemical fuel (an acid) caused a message to be relayed down the scaffold, and then the initial “off” state was recovered over time, due to the self-consumption of the fuel.
The results of the SQSig project will afford two publications in wide-interest chemistry journals.
- Chemically fuelled communication along a nanoscale molecular relay. Manuscript under preparation.
- Effect of intramolecular cooperativity on the formation of oligo-squaramide supramolecular polymers.
Those works will be published immediately Open Access, and preprints will be available from on-line repositories.
Scientific meetings have provided a significant opportunity to disseminate our research to our target audiences. Dr. Martínez-Crespo has presented the main results of this project in five conferences (in the UK, the Netherlands, France, Spain and online).
To contribute to the public understanding of science, Dr. Martínez-Crespo participated in the “Science is Wonderful! Activities”, delivering a talk (followed by a discussion) to four groups of secondary school students in Spain. Moreover, a divulgation poster was uploaded to the website of the “European Researchers Night – Catalan Section”.
SQ-OPE relays were prepared with different director groups in one end of their structure. We observed two opposite orientations of the SQ relays with respect to the OPE rigid rod. The orientation and robustness of the relay was dictated by the hydrogen-bonding properties of the director, thus determining the orientation and interaction capability of a remote SQ unit.
We installed a switchable director into a tris-SQ relay of 2 nm length (a distance similar to the thickness of the lipophilic region of a bilayer membrane). The resulting device responded to a simple chemical messenger, the proton, relaying the conformational change caused by protonation of the director to the end of the scaffold. Addition of a second messenger, a base, caused the recovery of the initial conformational state, which was able to accept subsequent protonation/deprotonation cycles.
The reversible communication device described above was then combined with a chemical fuel to produce an out-of-equilibrium system. The chemical fuel (an acid) caused a message to be relayed down the scaffold, and then the initial “off” state was recovered over time, due to the self-consumption of the fuel.
The results of the SQSig project will afford two publications in wide-interest chemistry journals.
- Chemically fuelled communication along a nanoscale molecular relay. Manuscript under preparation.
- Effect of intramolecular cooperativity on the formation of oligo-squaramide supramolecular polymers.
Those works will be published immediately Open Access, and preprints will be available from on-line repositories.
Scientific meetings have provided a significant opportunity to disseminate our research to our target audiences. Dr. Martínez-Crespo has presented the main results of this project in five conferences (in the UK, the Netherlands, France, Spain and online).
To contribute to the public understanding of science, Dr. Martínez-Crespo participated in the “Science is Wonderful! Activities”, delivering a talk (followed by a discussion) to four groups of secondary school students in Spain. Moreover, a divulgation poster was uploaded to the website of the “European Researchers Night – Catalan Section”.
Most artificial systems able to replicate allosteric regulation are based on semiflexible oligomers that form well-defined intramolecular hydrogen-bonding patterns. This project applies, for the first time, a rigid scaffold to develop a reversible communication relay with well-defined length and unambiguous alignment of the repeating units. The linearity and rigidity of the system makes it a good candidate for the development of artificial transmembrane communication devices.
A recent exciting challenge in Supramolecular Chemistry is the design of artificial molecular machines able to exploit chemical fuels to reach out-of-equilibrium conditions that replicate the conditions under which molecular machinery operates in cells. This project presents the first example of an artificial molecular communication relay operating under out-of-equilibrium conditions. Our device uses the energy stored in the signalling molecule (fuel) to perform a full operation cycle.
The development of synthetic systems able to replicate or even replace GPCRs in cell membranes remains an ultimate goal of this field of research. The potential biomedical implications of this field of research has clear resonance with the general public. For example, a recent high profile paper from Webb and Clayden in this area of synthetic signal transduction received widespread international publicity, and responses from the public indicated a high level of interest in using this technology to solve genetically linked GPCR defect that were causing illness in family members. The development of the SQ-OPE information relays is an advance on this previous work and provides another step closer to biomedical applications.
A recent exciting challenge in Supramolecular Chemistry is the design of artificial molecular machines able to exploit chemical fuels to reach out-of-equilibrium conditions that replicate the conditions under which molecular machinery operates in cells. This project presents the first example of an artificial molecular communication relay operating under out-of-equilibrium conditions. Our device uses the energy stored in the signalling molecule (fuel) to perform a full operation cycle.
The development of synthetic systems able to replicate or even replace GPCRs in cell membranes remains an ultimate goal of this field of research. The potential biomedical implications of this field of research has clear resonance with the general public. For example, a recent high profile paper from Webb and Clayden in this area of synthetic signal transduction received widespread international publicity, and responses from the public indicated a high level of interest in using this technology to solve genetically linked GPCR defect that were causing illness in family members. The development of the SQ-OPE information relays is an advance on this previous work and provides another step closer to biomedical applications.