A protein isoform is a version of a protein with only small differences to another isoform of the same protein. Different forms of a protein may be produced from different but related genes, or may arise from the same gene by alternative splicing. A large number of isoforms are caused by single nucleotide polymorphisms, small genetic differences between alleles of the same gene. The discovery of isoforms explains the apparently small number of coding genes revealed in the human genome project: the ability to create categorically different proteins from the same gene increases the diversity of the proteome. Isoforms are readily described and discovered by microarray studies and cDNA libraries.
Glycoforms
A glycoform is an isoform where different ways of a glycoprotein have different polysaccharides attached to them, by either posttranslational or cotranslational modifications.
Examples
- Creatine kinase, the presence of which in the blood can be used as an aid in the diagnosis of myocardial infarction, exists in 3 isoforms.
- Hyaluronan synthase, the enzyme responsible for the production of hyaluronan, has three isoforms in mammalian cells.
