Cullins are a family of hydrophobic proteins providing a scaffold for ubiquitin ligases (E3). All eukaryotes appear to have cullins. They combine with RING proteins to form Cullin-RING ubiquitin ligases (CRLs) that are highly diverse and play a role in a myriad of cellular processes.
Cullin-RING ubiquitin ligases (CRLs), such as Cul1 (SCF) play an essential role in targeting proteins for ubiquitin-mediated destruction; as such, they are diverse in terms of composition and function, regulating many different processes from glucose sensing and DNA replication to limb patterning and circadian rhythms. The catalytic core of CRLs consists of a RING protein and a cullin family member. For Cul1, the C-terminal cullin-homology domain binds the RING protein. The RING protein appears to function as a docking site for ubiquitin-conjugating enzymes (E2s). Other proteins contain a cullin-homology domain, such as the APC2 subunit of the anaphase-promoting complex/cyclosome and the p53cytoplasmic anchor PARC; both APC2 and PARC have ubiquitin ligase activity. The N-terminal region of cullins is more variable, and is used to interact with specific adaptor proteins.
With the exception of APC2, each member of the cullin family is modified by Nedd8 and several cullins function in Ubiquitin-dependent proteolysis, a process in which the 26S proteasome recognises and subsequently degrades a target protein tagged with K48-linked poly-ubiquitin chains. Nedd8/Rub1 is a small ubiquitin-like protein, which was originally found to be conjugated to Cdc53, a cullin component of the SCF (Skp1-Cdc53/CUL1-F-box protein) E3 Ub ligase complex in Saccharomyces cerevisiae (Baker's yeast), and Nedd8 modification has now emerged as a regulatory pathway of fundamental importance for cell cycle control and for embryogenesis in metazoans. The only identified Nedd8 substrates are cullins. Neddylation results in covalent conjugation of a Nedd8 moiety onto a conserved cullin lysineresidue.
^Kipreos ET, Lander LE, Wing JP, He WW, Hedgecock EM (June 1996). "cul-1 is required for cell cycle exit in C. elegans and identifies a novel gene family". Cell85 (6): 829–39. doi:10.1016/S0092-8674(00)81267-2. PMID8681378.
^Zheng N, Schulman BA, Song L, Miller JJ, Jeffrey PD, Wang P, Chu C, Koepp DM, Elledge SJ, Pagano M, Conaway RC, Conaway JW, Harper JW, Pavletich NP (April 2002). "Structure of the Cul1-Rbx1-Skp1-F boxSkp2 SCF ubiquitin ligase complex". Nature416 (6882): 703–9. doi:10.1038/416703a. PMID11961546.
^Goldenberg SJ, Cascio TC, Shumway SD, Garbutt KC, Liu J, Xiong Y, Zheng N (November 2004). "Structure of the Cand1-Cul1-Roc1 complex reveals regulatory mechanisms for the assembly of the multisubunit cullin-dependent ubiquitin ligases". Cell119 (4): 517–28. doi:10.1016/j.cell.2004.10.019. PMID15537541.
^Pan ZQ, Kentsis A, Dias DC, Yamoah K, Wu K (March 2004). "Nedd8 on cullin: building an expressway to protein destruction". Oncogene23 (11): 1985–97. doi:10.1038/sj.onc.1207414. PMID15021886.