WANI Dictionary

Isoform

Isoforms traditionally refer to proteins that are similar to each other and have similar functions.

In some cases, a single gene can encode multiple isoforms by alternative splicing (splicing isoforms). In other cases, multiple genes are responsible for the isoforms.

Recently, this term is also used for genes. The use of “protein isoforms” and “gene isoforms” is recommended for better clarification.

Definitions in the literature

• Protein isoforms – proteins that are similar to each other and perform similar roles within cells – have played an important role in the generation of biological diversity throughout evolution. In some cases a single gene can encode two or more isoforms by exploiting a process called alternative splicing. In other cases two or more closely related genes are responsible for the isoforms [5].
• ... any of two or more functionally similar proteins that have a similar but not an identical amino acid sequence [4].

Search for the definition from Wikipedia has stall out. There may be a definition by IUPAC that distinguishes isoform and protein modification (protein species), but I could not get the definition.

• A protein isoform, or "protein variant" is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences [1].
• The above Wikipedia definition refers to Schlüter et al. (2009) [2], and this paper further cites an IUPAC rule – "According to the IUPAC rules the term "isoform" is to be used for genetic variations such as allelic forms."
• The IUPAC rules [3], however, appear to define "isozyme" and "isoenzyme." No "isoform" can be seen in the reference.