Cullins are a class of scaffold proteins, which are part of the SCF (Skp1/Cullin/F-box protein) ubiquitin ligases. The activity of these ligases is positively regulated by the neddylation of the cullin while binding of the cullin to Cand1 (cullin-associated Nedd8-dissociated protein 1) favors the disassembly and impairs the reassembly of the complex. Cand1 blocks the neddylation site in the C-terminal part of cullin as well as the Skp1 adaptor binding site in the N-terminal region of cullin. In Aspergillus nidulans, the gene encoding the putative homolog of Cand1 is split into two genes (candA-N and candA-C) encoding two proteins each with one cullin binding site. Deletion of either gene causes an impairment of the asexual cycle, a block of the sexual cycle and the production of brownish-red pigments. These defects can be complemented by a candA-N::C fusion construct. Both CandA proteins interact with each other, but only CandA-C associates with cullins in a yeast two-hybrid assay indicating that CandA-N binding to cullin is mediated by CandA-C. In vivo, CandA-N requires CandA-C for transport into the nucleus. Binding of only CandA-C to cullin might reflect transient states in the disassembly/reassembly cycle of SCF ubiquitin ligases which could be adopted independently of cullin deneddylation.
Full conference title:
6th International Aspergillus Meeting
- Asperfest 6 (2009)