Editing Protein isoform (section)

== Characteristics ==
Generally, one protein isoform is labeled as the canonical sequence based on criteria such as its prevalence and similarity to [[Sequence homology|orthologous]]—or functionally analogous—sequences in other species.<ref>{{cite journal | vauthors = Li HD, Menon R, Omenn GS, Guan Y | title = Revisiting the identification of canonical splice isoforms through integration of functional genomics and proteomics evidence | journal = Proteomics | volume = 14 | issue = 23–24 | pages = 2709–18 | date = December 2014 | pmid = 25265570 | pmc = 4372202 | doi = 10.1002/pmic.201400170 | url = https://deepblue.lib.umich.edu/bitstream/2027.42/109787/1/pmic7911.pdf }}</ref> Isoforms are assumed to have similar functional properties, as most have similar sequences, and share some to most exons with the canonical sequence. However, some isoforms show much greater divergence (for example, through [[trans-splicing]]), and can share few to no exons with the canonical sequence. In addition, they can have different biological effects—for example, in an extreme case, the function of one isoform can promote cell survival, while another promotes cell death—or can have similar basic functions but differ in their sub-cellular localization.<ref>{{cite journal | vauthors = Sundvall M, Veikkolainen V, Kurppa K, Salah Z, Tvorogov D, van Zoelen EJ, Aqeilan R, Elenius K | title = Cell death or survival promoted by alternative isoforms of ErbB4 | journal = Molecular Biology of the Cell | volume = 21 | issue = 23 | pages = 4275–86 | date = December 2010 | pmid = 20943952 | pmc = 2993754 | doi = 10.1091/mbc.E10-04-0332 }}</ref> A 2016 study, however, functionally characterized all the isoforms of 1,492 genes and determined that most isoforms behave as "functional alloforms." The authors came to the conclusion that isoforms behave like distinct proteins after observing that the functional of most isoforms did not overlap.<ref>{{cite journal | vauthors = Yang X, Coulombe-Huntington J, Kang S, Sheynkman GM, Hao T, Richardson A, Sun S, Yang F, Shen YA, Murray RR, Spirohn K, Begg BE, Duran-Frigola M, MacWilliams A, Pevzner SJ, Zhong Q, Trigg SA, Tam S, Ghamsari L, Sahni N, Yi S, Rodriguez MD, Balcha D, Tan G, Costanzo M, Andrews B, Boone C, Zhou XJ, Salehi-Ashtiani K, Charloteaux B, Chen AA, Calderwood MA, Aloy P, Roth FP, Hill DE, Iakoucheva LM, Xia Y, Vidal M | display-authors = 6 | title = Widespread Expansion of Protein Interaction Capabilities by Alternative Splicing | journal = Cell | volume = 164 | issue = 4 | pages = 805–17 | date = February 2016 | pmid = 26871637 | pmc = 4882190 | doi = 10.1016/j.cell.2016.01.029 }}</ref> Because the study was conducted on cells ''in vitro'', it is not known if the isoforms in the expressed human proteome share these characteristics. Additionally, because the function of each isoform must generally be determined separately, most identified and predicted isoforms still have unknown functions.