Twinkle (protein) explained

Twinkle protein also known as twinkle mtDNA helicase is a mitochondrial protein that in humans is encoded by the TWNK gene (also known as C10orf2 or PEO1) located in the long arm of chromosome 10 (10q24.31).^{[1] [2] [3] [4]}

Twinkle is a mitochondrial protein with structural similarity to the phage T7 primase/helicase (GP4) and other hexameric ring helicases. The twinkle protein colocalizes with mtDNA in mitochondrial nucleoids, and its name derives from the unusual localization pattern reminiscent of twinkling stars. A homolog is found in Arabidopsis thaliana chloroplast and mitochondria.^[5]

Discovery

In 2001, a team was able to identify the C10orf2 gene and named it twinkle due to its localization pattern that resembles twinkling stars. The presumed main function of twinkle is important for the lifetime regulation of the human mtDNA. The gene is expressed at high levels in skeletal muscles. The gene encodes for a protein that has a full-length of 684 units of amino acids. The twinkle protein consists of 3 functional domains: a 5-primase domain, a linker region, and a helicase region. The linker and helicase regions are involved in most of the pathogenic mutations.

Function

The TWNK gene makes two proteins, Twinkle and Twinky. The proteins Twinkle and Twinky are both found in the mitochondria.^[6] Each mitochondrion contains a small amount of DNA which is known as mitochondrial DNA (mtDNA). The Twinkle protein is involved in the production of mtDNA by functioning as an adenine nucleotide dependent DNA helicase, an enzyme that binds to DNA and temporarily unwinds the double helix of the DNA molecule so that it can replicate.^[6] They also serve as primases able to initiate DNA replication.

They function as hexameric or heptameric DNA helicases, which unwinds the double-stranded DNA in the 5’ to 3’ direction in short segments. The proteins unwind single-stranded mitochondrial DNA binding protein and mtDNA polymerase gamma. These enzymes function similar to the T7 phage helicase (gp4); however, Twinkle and/ or Twinky are capable of both unwinding and recombining DNA making them bifunctional helicases.

Their functions as a helicase include the binding of both single stranded DNA (ssDNA) and double stranded DNA (dsDNA), and catalyzing DNA unwinding. The energy required for DNA unwinding is supplied by the hydrolysis of ATP to ADP. It has different binding affinities for each of its specific binding sites when binding either the ssDNA or the dsDNA.

Disease association

Mutations occurring on the TWNK gene are associated with health conditions such as Perrault Syndrome, ataxia neuropathy spectrum, infantile-onset spinocerebellar ataxia, and most prominently progressive external ophthalmoplegia.^[6]

One of the best known mutations of this gene is associated with infantile onset spinocerebellar ataxia or IOSCA.^[7] IOSCA is a neurodegenerative disease whose symptoms appear in children after one year of age. The symptoms of this disease include ataxia, muscle hypertonia, loss of deep-tendon reflexes, and athetosis and later on in the child's life hearing loss, psychotic behavior, sensory axonal neutrophil ataxia, and additional neurological development problems.^[8] Before age one, a child develops normally and then the child starts to experience neurological deficits.

Clinical significance

The twinkle gene is an important protein that is involved in the synthesis and maintenance of mtDNA. The gene is located in the mitochondrial matrix and mitochondrial nucleotides. Twinkle protein serves as the mitochondrial DNA helicase that binds to DNA and aids in unwinding the double helix of the DNA molecules. By allowing unwinding of the double helix, replication of mtDNA is achieved. Any form of mutation in twinkle protein can result in mtDNA disease. The disease can be categorized into two groups. The first category includes disease that impairs the respiratory function due to the primary mutation of the mtDNA; the second category is usually known as mtDNA maintenance disease. The cause of mtDNA maintenance diseases is the dysfunction of the replication and maintenance apparatus of mtDNA, programmed by nuclear genes. Infantile onset spinocerebellar ataxia (IOSCA) and progressive external ophthalmoplegia (PEO) are associated with multiple deletions of mtDNA.  PEO in humans and most mammals is associated with an eye disorder which involves the individual gradually losing the ability to move the eyes as well as the eyebrows. These disorders in recent times have been established to be occurring in the population, with the frequencies of single mutation projected to increase.

Transgenic mice expressing both human PEO patient mutations and the wild-type mouse twinkle protein have progressive respiratory chain dysfunction due to accumulation of mtDNA deletions, but the phenotype does not reduce lifespan.^[9]

References

Further reading

• Suomalainen A, Kaukonen J, Amati P, Timonen R, Haltia M, Weissenbach J, Zeviani M, Somer H, Peltonen L . An autosomal locus predisposing to deletions of mitochondrial DNA . Nature Genetics . 9 . 2 . 146–51 . February 1995 . 7719341 . 10.1038/ng0295-146 . 32160642 .
• Hirano M, DiMauro S . ANT1, Twinkle, POLG, and TP: new genes open our eyes to ophthalmoplegia . Neurology . 57 . 12 . 2163–5 . December 2001 . 11756592 . 10.1212/wnl.57.12.2163 . 42784334 .
• Lewis S, Hutchison W, Thyagarajan D, Dahl HH . Clinical and molecular features of adPEO due to mutations in the Twinkle gene . Journal of the Neurological Sciences . 201 . 1–2 . 39–44 . September 2002 . 12163192 . 10.1016/S0022-510X(02)00190-9 . 44270654 .
• Arenas J, Briem E, Dahl H, Hutchison W, Lewis S, Martin MA, Spelbrink H, Tiranti V, Jacobs H, Zeviani M . The V368i mutation in Twinkle does not segregate with AdPEO . Annals of Neurology . 53 . 2 . 278 . February 2003 . 12557300 . 10.1002/ana.10430 . 12656289 .
• Garrido N, Griparic L, Jokitalo E, Wartiovaara J, van der Bliek AM, Spelbrink JN . Composition and dynamics of human mitochondrial nucleoids . Molecular Biology of the Cell . 14 . 4 . 1583–96 . April 2003 . 12686611 . 153124 . 10.1091/mbc.E02-07-0399 .
• Agostino A, Valletta L, Chinnery PF, Ferrari G, Carrara F, Taylor RW, Schaefer AM, Turnbull DM, Tiranti V, Zeviani M . Mutations of ANT1, Twinkle, and POLG1 in sporadic progressive external ophthalmoplegia (PEO) . Neurology . 60 . 8 . 1354–6 . April 2003 . 12707443 . 10.1212/01.wnl.0000056088.09408.3c . 31209510 .
• Van Goethem G, Löfgren A, Dermaut B, Ceuterick C, Martin JJ, Van Broeckhoven C . Digenic progressive external ophthalmoplegia in a sporadic patient: recessive mutations in POLG and C10orf2/Twinkle . Human Mutation . 22 . 2 . 175–6 . August 2003 . 12872260 . 10.1002/humu.10246 . 35604757 . free .
• Deschauer M, Kiefer R, Blakely EL, He L, Zierz S, Turnbull DM, Taylor RW . A novel Twinkle gene mutation in autosomal dominant progressive external ophthalmoplegia . Neuromuscular Disorders . 13 . 7–8 . 568–72 . September 2003 . 12921794 . 10.1016/S0960-8966(03)00071-3 . 23020569 .
• Maria Falkenberg. Korhonen JA, Gaspari M, Falkenberg M . TWINKLE Has 5' -> 3' DNA helicase activity and is specifically stimulated by mitochondrial single-stranded DNA-binding protein . The Journal of Biological Chemistry . 278 . 49 . 48627–32 . December 2003 . 12975372 . 10.1074/jbc.M306981200 . 12598297 . free .
• Korhonen JA, Pham XH, Pellegrini M, Falkenberg M . Reconstitution of a minimal mtDNA replisome in vitro . The EMBO Journal . 23 . 12 . 2423–9 . June 2004 . 15167897 . 423294 . 10.1038/sj.emboj.7600257 .
• Wanrooij S, Luoma P, van Goethem G, van Broeckhoven C, Suomalainen A, Spelbrink JN . Twinkle and POLG defects enhance age-dependent accumulation of mutations in the control region of mtDNA . Nucleic Acids Research . 32 . 10 . 3053–64 . 2004 . 15181170 . 434440 . 10.1093/nar/gkh634 .
• Tyynismaa H, Sembongi H, Bokori-Brown M, Granycome C, Ashley N, Poulton J, Jalanko A, Spelbrink JN, Holt IJ, Suomalainen A . Twinkle helicase is essential for mtDNA maintenance and regulates mtDNA copy number . Human Molecular Genetics . 13 . 24 . 3219–27 . December 2004 . 15509589 . 10.1093/hmg/ddh342 . free .
• Hudson G, Deschauer M, Busse K, Zierz S, Chinnery PF . Sensory ataxic neuropathy due to a novel C10Orf2 mutation with probable germline mosaicism . Neurology . 64 . 2 . 371–3 . January 2005 . 15668446 . 10.1212/01.WNL.0000149767.51152.83 . 36540686 .
• Ziebarth TD, Farr CL, Kaguni LS . Modular architecture of the hexameric human mitochondrial DNA helicase . Journal of Molecular Biology . 367 . 5 . 1382–91 . April 2007 . 17324440 . 2711006 . 10.1016/j.jmb.2007.01.079 .
• Baloh RH, Salavaggione E, Milbrandt J, Pestronk A . Familial parkinsonism and ophthalmoplegia from a mutation in the mitochondrial DNA helicase twinkle . Archives of Neurology . 64 . 7 . 998–1000 . July 2007 . 17620490 . 10.1001/archneur.64.7.998 .
• Sarzi E, Goffart S, Serre V, Chrétien D, Slama A, Munnich A, Spelbrink JN, Rötig A . Twinkle helicase (PEO1) gene mutation causes mitochondrial DNA depletion . Annals of Neurology . 62 . 6 . 579–87 . December 2007 . 17722119 . 10.1002/ana.21207 . 30878068 .
• Ołdak M, Oziębło D, Pollak A, Stępniak I, Lazniewski M, Lechowicz U, Kochanek K, Furmanek M, Tacikowska G, Plewczynski D, Wolak T, Płoski R, Skarżyński H . Novel neuro-audiological findings and further evidence for TWNK involvement in Perrault syndrome . Journal of Translational Medicine . 15 . 1 . 25 . February 2017 . 28178980 . 5299684 . 10.1186/s12967-017-1129-4 . free .

Notes and References

1. Spelbrink JN, Li FY, Tiranti V, Nikali K, Yuan QP, Tariq M, Wanrooij S, Garrido N, Comi G, Morandi L, Santoro L, Toscano A, Fabrizi GM, Somer H, Croxen R, Beeson D, Poulton J, Suomalainen A, Jacobs HT, Zeviani M, Larsson C . 6 . Human mitochondrial DNA deletions associated with mutations in the gene encoding Twinkle, a phage T7 gene 4-like protein localized in mitochondria . Nature Genetics . 28 . 3 . 223–31 . July 2001 . 11431692 . 10.1038/90058 . 22237030 .
2. Leipe DD, Aravind L, Grishin NV, Koonin EV . The bacterial replicative helicase DnaB evolved from a RecA duplication . Genome Research . 10 . 1 . 5–16 . January 2000 . 10645945 . 10.1101/gr.10.1.5 . 31 January 2024 .
3. Nikali K, Suomalainen A, Saharinen J, Kuokkanen M, Spelbrink JN, Lönnqvist T, Peltonen L . Infantile onset spinocerebellar ataxia is caused by recessive mutations in mitochondrial proteins Twinkle and Twinky . Human Molecular Genetics . 14 . 20 . 2981–90 . October 2005 . 16135556 . 10.1093/hmg/ddi328 . free .
4. Web site: Entrez Gene: PEO1 progressive external ophthalmoplegia 1.
5. Diray-Arce . J . Liu . B . Cupp . JD . Hunt . T . Nielsen . BL . The Arabidopsis At1g30680 gene encodes a homologue to the phage T7 gp4 protein that has both DNA primase and DNA helicase activities. . BMC Plant Biology . 4 March 2013 . 13 . 36 . 10.1186/1471-2229-13-36 . 23452619. 3610141 . free .
6. Web site: TWNK gene . Genetics Home Reference .
7. Web site: TWNK twinkle mtDNA helicase [Homo sapiens (human)] - Gene ]. NCBI .
8. Book: Lönnqvist T . Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJ, Stephens K, Amemiya A . Infantile-Onset Spinocerebellar Ataxia (IOSCA) . GeneReviews . 171–178 . 2016 . University of Washington, Seattle . 20301746 . https://www.ncbi.nlm.nih.gov/books/NBK3795/ .
9. Tyynismaa H, Mjosund KP, Wanrooij S, Lappalainen I, Ylikallio E, Jalanko A, Spelbrink JN, Paetau A, Suomalainen A . 2005 . Mutant mitochondrial helicase Twinkle causes multiple mtDNA deletions and a late-onset mitochondrial disease in mice . Proc Natl Acad Sci U S A . 102 . 49. 17687–92 . 16301523 . 10.1073/pnas.0505551102 . 1308896 . 2005PNAS..10217687T . free .