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Synchronous Fuete: Biological Motors in Nanotechnology



In the vast expanses of our galaxy, many secrets are hidden that scientists from around the world are trying so hard to find and unravel. However, it is not necessary for something to be big in order to be mysterious. A vivid proof of this is the world lying at the cellular level. Many of the most diverse in form, structure, functional and purpose of cells together fulfill a common task - maintaining the body's life. If you exaggerate, then the cells, like people, have professions: postmen, transmitting information between cells and tissues; border guards who identify and fight infections; archivists collecting and storing information, etc. In this incredible range of specialties, there is a very unusual, at least for us, profession - a biological motor, which generates the mechanical force necessary for the movement of cells.

These cells are particularly interesting in the context of nanotechnology. Previously, there was a problem in the implementation of a workable nano-device based on biological motors - motors must be integrated into larger systems so that their mechanical movements can be effectively connected with other molecular units. Scientists from the University of Munich (Germany) managed to get closer to the implementation of this concept. What specific cells and molecular units were used in creating the model, how was their work controlled, what was the task of the working system and what results did it show? We will find answers to these questions in the report of the research group. Go.

Study basis


As mentioned above, a biological motor is a cell that generates the mechanical force necessary to realize the movement of cells, as well as intracellular transport. These motors include motor proteins and protein complexes.

In order to carry out its non-standard activities, motor proteins, like any machine, need fuel. Adenosine triphosphoric acid (ATP, C 10 H 16 N 5 O 13 P 3 ) plays its role . ATP is a universal source of energy for all biological processes within living systems.

Motor proteins function by hydrolysis * ATP, which allows proteins to convert chemical energy into mechanical work.
Hydrolysis * is the reaction of exchange decomposition between a dissolved substance and a solvent, in which the decomposition of a substance (in this case ATP) and water occurs with the formation of new compounds.
In particular, motor proteins include myosins, kinesins and dyneins. Myosins make up about 40-60% of all muscle proteins, participating in the process of muscle contraction.

Kinesins, which became a scientific meme several years ago, travel through microtubules (protein intracellular structures), participating in the processes of mitosis, meiosis and vesicular transport.


Video demonstration of how kinesin moves through a microtubule, transformed into a meme. (the original is taken from The Inner Life of a Cell ; the music overlaid on the video is Stayin 'Alive, Bee Gees, 1977).

Dyneins, like kinesins, also move along the microtubules of the cytoskeleton, participating in the process of cargo transfer (vesicles, mitochondria, etc.).

The interest in biomotors by nanotechnologists is due to several important factors: nanoscale, biocompatibility and the ability to use genetic engineering to create biomotors with specified functions.

At the moment, there are a number of developments based on the principles of action of biological motors. However, information regarding how much real work a single molecular motor can do is not yet sufficient for full implementation. Another puzzle for scientists is the question of how to integrate the molecular motion block into a larger structure so that its directed movement is effectively transformed into an increase in potential energy at remote points in the structure.

Obviously, there are many obstacles, but this has never stopped scientists. In the study we are considering today, scientists describe molecular installation 1, which allows the transfer of potential energy from the motor unit to a remote receiver unit, thereby accelerating the movement of the latter (image No. 1).


Image No. 1

The role of the receiver unit was played by axial-chiral * biaryl * , which in its non-tethered form (model system 2) undergoes a slow and non-directional rotation of atropisomerization in the direction of equilibrium of enantiomers 1: 1 ( 1a ).
Axial chirality * arises as a result of a nonplanar arrangement of substituents relative to some axis — the axis of chirality.
Biaryl * - Any compound containing a substructure, which is a combination of two aromatic compounds or aryl groups, if they are connected by a single bond.
The conjugation of the molecular motor block allows unidirectional to divert this atropisomerization from equilibrium. As a result, the atropisomerization of biaryl is no longer passive (following the operation of the motor), but represents an energy obstacle against which the motor must actively work.

In machine 1, an increase in the rate of atropisomerization of biaryl by several orders of magnitude is achieved by the action of a motor that suppresses internal barriers to the isolated rotation of biaryl (model system 2 by 1b and 1s ).

Molecular Installation 1 includes a molecular motor unit based on HTI, which belongs to the class of indigo chromophores. This type of unit is extremely sensitive to light, i.e. thanks to the light, it can be controlled. The motor block is covalently connected to a remote biaryl axis, which does not move with the rotation of the motor.

One of the differences between this installation and its earlier versions is the presence of additional states (steps): the earlier version had 4 states and was regulated only by the rotation steps of the motor; a new option is a six-speed system (image No. 2).


Image No. 2

Six isomeric states are named as follows: AT for stress state A; AR for relaxed state A, as well as BR, CT, CR, and DR (intermediate states of the system).

Five of these steps can be observed experimentally, which confirms the presence of the sixth step and, therefore, confirms the full directionality for 360 degrees rotation of the associated system of the block motor and the block receiver.

The motor system 1 was synthesized by the convergent method due to the brominated HTI precursor, to which a covalent bond containing the function of the boronic ester was attached via a copper catalyzed click reaction.

Subsequently, the Suzuki reaction * gives macrocyclization * , followed by oxidation to give the final structure 1.
The Suzuki reaction * is an organic reaction of aryl and vinylboronic acids with aryl or vinyl halides, catalyzed by Pd (0) complexes.
Macrocyclization * - a cyclization reaction that leads to the formation of a macrocycle, i.e. a chemical compound in which there are 9 or more bonded atoms forming a ring.
For the two most stable states of AR and CR of system 1 and the most stable state of system 2, crystals suitable for structural analysis were obtained (®-configured isomers of racemic * AR at 1d ; CR at 1e ).
Racemat * is an equimolar mixture of two stereoisomers, which are mirror images of each other. The racemic compound consists of crystals, in each of which there are molecules of both enantiomers, and their ratio is 1: 1.
Since AR / AT and CR can be separated using HPLC (high performance liquid chromatography), their behavior under conditions of heating and irradiation at different temperatures can be studied independently. When the racemic CR solution in (CDCl 2 ) 2 was heated to 80 ° C - 140 ° C, more stable AR was formed in 93% of cases. This sets the difference in free enthalpy ∆G = 1.8–1.9 kcal / mol in this temperature range between these two states. Corresponding kinetic analysis revealed a high-energy barrier of 28.2 kcal / mol at 80 ° C, accompanying the thermal isomerization of the Z / E double bond.

When cooling pure CR to -105 ° C in CD 2 Cl 2 / CS 2(ratio 4/1) and irradiating it with 450 nm light, a new set of signals appears, which differs from the known set of signals AR and AT ( 3a ).


Image No. 3

The signals of the DR isomer decay to 75% within 28 minutes at a temperature of -80 ° C and complete darkness, but the signals of the AT isomer increase, on the contrary ( 3 ).

Thermal equilibrium between DR (the remaining 12%) and AT (88%) is observed at -60 ° C, which is expressed in ∆G = 0.84 kcal / mol between the two states. Kinetic analysis of thermal decomposition revealed an accompanying free activation enthalpy ∆ ‡ G = 13.9 kcal / mol at -80 ° C for this process. At temperatures from -40 to 0 ° C, attenuation of AT signals and a concomitant increase in known AR signals are observed until equilibrium is reached between them. A kinetic analysis of this process determined ∆ ‡ G equal to from 18.4 to 19.3 kcal / mol at temperatures from –40 ... 0 ° C.

Thus, it was found that irradiation of CR leads to the first DR photoisomerization product, which is thermally converted to the AT isomer by inverting a single helix in the motor block. When cooling an equilibrium solution of AR / AT in CD 2Cl 2 / CS 2 up to -105 ° C and when it was irradiated with 450 nm light, the AR photoreaction was observed, due to its prevalence. A new set of signals also appears that differ from the already known CR ( 3f ) signals . These new signals, being the product of the AR photoreaction, confirm the expected direction of photoisomerization from AR to BR, which then stabilizes even more, undergoing rapid helical inversion to CT even at low temperature.

At a temperature of -80 ° C and in complete darkness, the BR / CT signals almost completely disappear, and only the CR signals continue to amplify further ( 3e ). This gives a lower limit for the energy difference between CT and CR equal to 0.98 kcal / mol.

Kinetic analysis determined ∆ ‡ G = 13.4–13.5 kcal / mol, which is necessary for the conversion of ST into CR. It can be seen that the activation energy of atropisomerization of CT in CR decreases compared to that for the atropisomerization of AT in AR (18.4 kcal / mol). This may be due to the higher stress (strain) in the CT compared to the AT, which may be due to the large distances between the two phenolic oxygen atoms, which serve as connection points of the linker chain in structures C, which is not in structures A. In the crystalline state, CR between two oxygen atoms is 10.6, while in AR it is 7.6. This gives the linker chain greater conformational (spatial position of atoms) freedom in the A-structures than in the C-structures. If we take into account the free activation enthalpy for the thermal transformation of CT into CR,then this conversion process can be completely stopped at -105 ° C.

At a temperature of -105 ° C, it is possible to check the degree of accumulation of CT during strong exposure to AR light. This is possible if the energy difference between BR and ST exceeds 2.0 kcal / mol and if the ST structure is not involved in any photochemistry processes by itself. However, CT accumulation during AR irradiation at -105 ° C is not possible, since there is rapid thermal equilibrium between CT and BR.


Table No. 1

The combination of the above observations and data allows you to create a mechanical picture of a 6-step sequence of unidirectional rotation in model 1 (image No. 2 and No. 4).


Image No. 4

Experiments with different temperature conditions allowed us to determine the temperature dependence of ∆G between CR and AR / AT, DR and AT, AT and AR, as well as the temperature dependence of ∆ G for BR / CT and CR, DR and AT, AT and AR (table no. 1).

Unlike the usual 4-speed mechanism based on the HTI motor, 360-degree full rotation includes two additional steps, which are the increase in potential energy transmitted from the motor to the biaryl block. During these two steps, an energy bond is formed between the motor and the biaryl block ( 4b ), i.e. the latter is no longer energetically degenerate.


Image No. 5

Instead, the energy of any of the atropisomers increases due to “ratchet” steps of the motor during one full rotation ( 5sand 5d ). This energy change provides up to 90% of the interconversion of the atropisomer at the following thermally activated stages and, therefore, almost complete rotation of the biaryl block during one working cycle of the mechanism.

This observation may indicate that the biaryl block has undergone an increase in potential energy, which is the result of the operation of the motor block. It is worth noting that the initial increase in energy is much larger than what reaches the biaryl block. So, only 72% of it is transmitted from the motor to the biaryl block.

The above observations suggest that the length of the connection between the motor and the biaryl block is an important aspect in the process of changing the degree of energy transfer. Therefore, a shorter connection may allow more potential energy to be transferred from BR and DR to AT and CT.

For a more detailed acquaintance with the nuances of the study, I recommend that you look into the report of scientists and additional materials to it.

Epilogue


In this work, scientists described the principle of operation of their invention, based on the interaction of biological motors and molecular elements. The developed installation allows you to transfer potential energy from the motor to a specific element (in this case, it is a biaryl block). As a result of motor activity, the thermal atropisomerization of biaryl is forced to proceed unidirectionally and at a faster rate. Energy transfer occurs during thermally activated ratchets (steps) in the rotation mechanism. It was also found that about 72% of the initial energy of the motor is transmitted to a given unit.

This invention is an important step towards the creation of complete biological nanometer devices. The use of bio-motors in the design of such mechanisms is due to their biocompatibility, ease of change in functionality due to genetic engineering, as well as their natural nanoscale. Artificial motors at the moment can not boast of the above combination of advantages.

Researchers say that the next step in their work will be to demonstrate that their installation is able to perform not only abstract actions, but also be useful. In other words, their future creation will be more refined to perform useful functions at the molecular level.

Thank you for your attention, remain curious and have a good working week, guys. :)

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Source: https://habr.com/ru/post/undefined/

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