Walker's A and B-box consensus sequences
Those sequences are nucleotide binding sites, e.g. in Apaf-1.
Loosely conserved set of sequences which is found in many regulatory proteins, including beta-subunits of heterotrimeric G proteins, the SREBP cleavage-activating protein, but also in Apaf-1. In Apaf-1, the WD-40 repeats have an inhibitory effect on caspase-9 activation by Apaf-1, which is relieved after cyto c binding in the presence of dATP, allowing the formation of a multimeric Apaf-1/cyto c complex.
The WW domain is a short motif that can bind phosphoserine or phosphothreonine residues. Its name derives from the presence of two conserved tryptophane residues. WW domains were identified in several members of the E3 ubiquitin ligase family, presumably contributing to substrate-specific binding and ubiquitination.
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