E2type

E2type is a term used in biochemistry and molecular biology to refer to the class of enzymes known as E2 ubiquitin-conjugating enzymes, a component of the ubiquitin-proteasome system. In many sources the phrase E2-type is informal; the standard nomenclature identifies these proteins as E2 enzymes (UBE2 family). The term is sometimes used in teaching materials or reviews to distinguish E2 enzymes from E3 ligases and E1 activating enzymes.

E2 enzymes play a central role in ubiquitination, a process that attaches ubiquitin molecules to substrates to regulate their stability, activity, or location. They function as intermediaries that receive activated ubiquitin from E1 and transfer it, often via interaction with E3 ligases, to substrates or to growing ubiquitin chains. E2s influence the type of ubiquitin linkage formed and can determine whether a substrate is monoubiquitinated or polyubiquitinated with specific linkage types.

Most E2 enzymes are small cytosolic proteins, typically around 15–25 kDa, with a catalytic cysteine that forms a thioester bond with ubiquitin. They pair with a variety of E3 ligases, and the combination of E2 and E3 dictates substrate specificity and chain topology. Notable examples include several UBE2D family members (UbcH5) and the UBE2N–UBE2V1/2 pair, which specialize in distinct ubiquitin linkages.

Dysregulation of E2 activity has been linked to diseases such as cancer and neurodegeneration, making E2-type enzymes a subject of interest for therapeutic targeting. However, the term E2type is not a formal taxonomic category and is primarily encountered as a descriptive or teaching label rather than an official nomenclature.

See also: Ubiquitin-proteasome system, E1 activating enzymes, E3 ligases.