Isoforme

Isoforme, more commonly called an isoform in English, refers to any of several related forms of a protein that come from the same gene. Isoforms may differ in amino acid sequence, length, subcellular localization, stability, or catalytic or binding activity. They can be produced by several molecular mechanisms, including alternative splicing of mRNA, use of alternative promoters, alternative transcription start sites, and differences in post-translational modification.

The production and distribution of isoforms enable tissues and developmental stages to tailor protein function. For example, different isoforms may be expressed in distinct cellular contexts or respond to signaling cues in ways that modulate activity, localization, or interactions with other molecules. Isoforms are distinct from paralogous proteins or different enzymes that catalyze the same chemical reaction (isozymes), though all relate to the same gene family. Misregulation of isoform expression or aberrant splicing is associated with a range of diseases, including cancer and neurodegenerative disorders, and can influence disease progression and treatment response.

Detection and study of isoforms rely on transcriptomic and proteomic approaches that resolve variant sequences and modifications, such as RNA sequencing and mass spectrometry. Nomenclature for isoforms varies by gene and database, commonly using suffixes or transcript identifiers to distinguish variants. Therapeutic strategies increasingly target isoform-specific features, including splice-switching approaches that shift the balance of isoforms to achieve a desired cellular outcome.