Ropes have superhelical structuresAn illustration showing the superhelical structure of chromatin
A superhelix is a molecular structure in which a helix is itself coiled into a helix. This is significant to both proteins and genetic material, such as overwound circular DNA.
The earliest significant reference in molecular biology is from 1971, by F. B. Fuller:
A geometric invariant of a space curve, the writhing number, is defined and studied. For the central curve of a twisted cord the writhing number measures the extent to which coiling of the central curve has relieved local twisting of the cord. This study originated in response to questions that arise in the study of supercoiled double-stranded DNA rings.[1]
About the writhing number, mathematician W. F. Pohl says:
It is well known that the writhing number is a standard measure of the global geometry of a closed space curve.[2]
Contrary to intuition, a topological property, the linking number, arises from the geometric properties twist and writhe according to the following relationship:
Lk= T + W,
where Lk is the linking number, W is the writhe and T is the twist of the coil.
The linking number refers to the number of times that one strand wraps around the other. In DNA this property does not change and can only be modified by specialized enzymes called topoisomerases.
^Fuller, F. Brock (1971). "The writhing number of a space curve" (PDF). Proceedings of the National Academy of Sciences. 68 (4): 815–819. Bibcode:1971PNAS...68..815B. doi:10.1073/pnas.68.4.815. MR 0278197. PMC 389050. PMID 5279522.
^Pohl, William F. (1968). "The self-linking number of a closed space curve". Journal of Mathematics and Mechanics. 17 (10): 975–985. doi:10.1512/iumj.1968.17.17060. MR 0222777.
A superhelix is a molecular structure in which a helix is itself coiled into a helix. This is significant to both proteins and genetic material, such as...
to it, a right-handed superhelix. The "relaxed" structure on the left is not found unless the chromosome is nicked; the superhelix is the form usually found...
stabilizing the entire triple helix. The rise of the collagen helix (superhelix) is 2.9 Å (0.29 nm) per residue. The center of the collagen triple helix...
proteins wraps DNA around itself in about 1.7 turns of a left-handed superhelix. In 1997 the first near atomic resolution crystal structure of the nucleosome...
repeating beta strands subunits, arranged in antiparallel fashion to form a superhelix. Beta solenoids are part of the solenoid class of protein tandem repeats...
commonly helix-turn-helix motifs, arranged in antiparallel fashion to form a superhelix. Alpha solenoids are known for their flexibility and plasticity. Like...
to the overall free energy of the triple helix. The formation of the superhelix not only protects the critical glycine residues on the interior of the...
a single type of unit. Such dimeric structures can stack into a tall superhelix ("hypernucleosome") onto which DNA coils in a manner similar to nucleosome...
domain consists of a core of 6 elements: 4 beta-sheets forming an extended superhelix; 2 flanking elements that tend to include some alpha helix. The sheets...
at 3.1 ˚A resolution: a tripartite protein assembly and a left-handed superhelix". PNAS. 88 (22): 10148–52. Bibcode:1991PNAS...8810148A. doi:10.1073/pnas...
trimers), the core of which consists of 4 turns of a (beta/beta/alpha)n superhelix. Some enzymes in the superfamily have been shown to display dehalogenase...
motif. Repeats of more than three TPR motifs generate a right handed superhelix characterized by both a concave and a convex face, of which the concave...
supercoiled molecule into a fully relaxed form, then to positively coiled superhelix at maximum intercalation. Agarose gel electrophoresis can be used to resolve...
the crystal structure of β-catenin, where the 12 tandem repeats form a superhelix of alpha helices with three helices per unit. The cylindrical structure...
lipid transfer proteins consist of 4 alpha-helices in a right-handed superhelix with a folded leaf topology. The structure is stabilised by disulfide...
very-short-patch DNA repair endonuclease bound to its reaction product-site in a DNA superhelix". Nucleic Acids Res. 31 (6): 1633–9. doi:10.1093/nar/gkg273. PMC 152875...
beta-catenin-like-repeat, is about a 40 amino acid long tandem repeat that forms superhelix of helices. Another feature is that TMCO6 has an Arginine rich region...
revealed that it consists of eight helices arranged in a double-layer superhelix. The existence of conserved patches of residues on the domain surface...
Similarly, the genome of clavavirus APBV1 is packaged in a tight, left-handed superhelix with its major capsid proteins, reflecting an adaptation allowing for...
et al. (1999). "Clathrin self-assembly is mediated by a tandemly repeated superhelix". Nature. 399 (6734): 371–5. Bibcode:1999Natur.399..371Y. doi:10.1038/20708...
88 °C and pH 2.5. Virions are non-enveloped, consisting of a tube-like superhelix formed by dsDNA and the major structural protein, with plugs at each end...
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