RING finger-E2 Interactions

One point that arises from study of these E2-E3 structures, is that there is a degree of specificity in their physical interactions. The biochemical data extends the idea of physical specificity in E2-E3 interactions to functional specificity. An example of this is the Brcal-Bardl heterodimer, which interacts physically with UbcH7 and UbcHSC, but is only active with UbcHSC. There appear to be two consequences of E2 specificity variability in the strength of a particular E3 response and variability in the type of ubiquitin modification. 

The Snurf (small nuclear RING finger) protein has E3 activity using at least six different E2s [80], all of which appear to have different patterns of ubiquitin modification. On the other hand A07 and Brcal only appear active with members of the 

UbcH5 family [21, 80, 81]. Presumably, the ability to interact productively with a smaller number of E2s will restrict E3 activity to situations where the RING finger protein and the E2 are co-expressed and co-localized. 

Other Protein-Protein Interaction Motifs in RING finger Proteins 

RING finger proteins may have other domains associated with signal transduction, such as SH3 and STAT domains and domains that bind and effect hydrolysis of nucleotides in signal transduction or for other purposes. These include ATPases, ATP synthases, serine/threonine kinases, GTP-binding domains, ADP-ribosylation domains and AAA-superfamily ATPases (http //home.cancer.gov/lpds/weissman). 

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