How do Hect and RING ligases differ?

Unlike the HECT domain, the RING finger domain does not form a catalytic intermediate with ubiquitin. Instead, the RING finger serves, at a minimum, as a scaffold that brings E2 and substrate together, and at least one study suggests that RING finger domains can also allosterically activate E2s (Ozkan et al., 2005).

What is meant by ligase?

ligase. / (ˈlaɪˌɡeɪz) / noun. any of a class of enzymes that catalyse the formation of covalent bonds and are important in the synthesis and repair of biological molecules, such as DNA.

How are ring-type E3 ligases different from other ligases?

RING-type E3s constitute a large and diverse class of ubiquitin ligases. RING-type E3s exist as monomers, dimers, and in complex multi-subunit assemblies. RING-type E3s recognize substrates by a variety of mechanisms. Recent structural studies have provided insight into how RINGs function with E2s.

Are there any E3 ligases in CUL2 complexes?

The RING Domain as an E2 recruitment domain revealed a large family of E3 ligases. P urification of Cul2 complexes by the Conaway lab identified a conserved RING domain protein we named Rbx1 (also known as Roc1), that our and Wade Harper’s labs showed to be required for SCF function in vitro and in vivo in yeast (110, 111) .

How are E3 ligases used in ubiquitin transfer?

E3s function by one of two general mechanisms. They serve either as catalytic intermediates in ubiquitination, akin to E1 and E2, or they mediate the transfer of ubiquitin directly from E2~Ub to substrate. The former mechanism is used by Homologous to E6-AP Carboxy Terminus (HECT)-type E3s (reviewed in this issue by Martin et al).

Where does the ring-type domain bind the E2?

In all available E2:E3 structures, the RING-type domain binds the E2 on a surface that is remote from the active site Cys (and therefore from the ubiquitin thioester) . The non-contiguous E3-binding and active sites on the E2 imply that the role played by a RING to facilitate ubiquitin transfer may be indirect and, therefore, allosteric.