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Globular actin (G-actin) is a monomer that is composed of a larger cleft (active site) and a smaller cleft (allosteric site). are hydrophilic residues of active site. The tertiary structure consists of four major subdomains. form the smaller cleft and form the larger cleft. The active site is located within subdomain 2. It is filamentous when polymerized (F-actin).^[1]

Function

G-actin can be polymerized to form filamentous F-actin. It is involved in cell motility in prokaryotic and eukaryotic cells. It builds a ladder on which the myosin filament climbs, which in turn causes muscle contractions and other cell movements. It also maintains structure and makes up some of the cytoskeleton of the cell. It orients cellular processes based on space and time.^[2]

Relevance and applications

Parallel Computation Using Actin Fibers and Myosin II Motors

Electronic computers are able to follow a linear path to use sequential logic to perform high volumes of operations at respectable speeds. However, given a challenge such as a nondeterministic polynomial time complete (NP-complete) problem, such machines fail to provide the correct answer in a reasonable time. NP-complete problems are defined as mathematical problems that can be solved by a “parallel” Turing machine that can perform many computations simultaneously. In this aspect, modern computers are limited by the heat production and the number of parallel computations they can perform, although the advent of multi-core CPUs partially alleviates the problem.

Actin provides unique advantages that make this solution more dependable, flexible, and scalable than alternatives. Actin is self-propelled, operates independently, and has small dimensions which makes it able to explore the dense grid network in a parallel manner. ATP is used to power the computation, which eliminates the need of an electric potential to be delivered from a single point of access, which makes powering larger SSP computations realistic. The molecular motor attached to the F-actin is also much more power efficient than traditional computers, effectively eliminating heat dissipation limitations.^[3] The actin design can be mass produced as a computing agent for all NP-complete problems since the nature of the problem is inherently encoded into the grid network. Furthermore, actin can also replenish itself through enzymatic splitting and elongation.

The preliminary test run on a 3 number SSP provides error rate too high to be within a reasonable margin of error for SSPs with more than 10 numbers (Fig. 4). The error is a direct result of the failure of pass junctions to force 100% of F-actin to traverse in a straight path.^[4] Still, the success rate for SSPs with less than 10 variables is acceptable enough to be a viable method of parallel computation.

References

https://www.rcsb.org/structure/3hbt http://proteopedia.org/wiki/index.php/Non-polymerizable_monomeric_actin https://docs.google.com/presentation/d/1DNBY9ykH7yl9MO4QSp4G86HEyhbMvznpBvlZs_rGOCY/edit#slide=id.g29fda9e754_0_0 https://docs.google.com/document/d/1Yw_4G4XPA5Wu2AUTeDVvhgyO6cSQvjp9S_RxfgUIwXY/edit?ts=5a984750

1. ↑ doi: https://dx.doi.org/10.2210/rcsb_pdb/mom_2001_7
2. ↑ Dominguez R, Holmes KC. Actin structure and function. Annu Rev Biophys. 2011;40:169-86. doi: 10.1146/annurev-biophys-042910-155359. PMID:21314430 doi:http://dx.doi.org/10.1146/annurev-biophys-042910-155359
3. ↑ Nicolau DV Jr, Lard M, Korten T, van Delft FC, Persson M, Bengtsson E, Mansson A, Diez S, Linke H, Nicolau DV. Parallel computation with molecular-motor-propelled agents in nanofabricated networks. Proc Natl Acad Sci U S A. 2016 Mar 8;113(10):2591-6. doi:, 10.1073/pnas.1510825113. Epub 2016 Feb 22. PMID:26903637 doi:http://dx.doi.org/10.1073/pnas.1510825113
4. ↑ Nicolau DV Jr, Lard M, Korten T, van Delft FC, Persson M, Bengtsson E, Mansson A, Diez S, Linke H, Nicolau DV. Parallel computation with molecular-motor-propelled agents in nanofabricated networks. Proc Natl Acad Sci U S A. 2016 Mar 8;113(10):2591-6. doi:, 10.1073/pnas.1510825113. Epub 2016 Feb 22. PMID:26903637 doi:http://dx.doi.org/10.1073/pnas.1510825113