Repeating motifs sequence homology

WD repeats were, in a way, where the coronin story started and so I can t end this review without a word about the structure of coronins. The archetypal WD repeat proteins are the Gp subunits, which have seven repeats and fold into a seven-bladed P-propeller. Although motif searches only identify five canonical WD repeats in coronins, the crystal structure of coronin 1A has shown that there are two cryptic WD repeats and that like the Gp subunits, the protein folds into a seven-bladed P-propeller structure. So while coronin did not turn out to be a direct link between G-protein coupled receptors and the cytoskeleton, they have turned out to be more structurally similar to the Gp subunits than was originally thought based on sequence homology. 

Fig. 5. Domain structure of Hsp70 co-chaperones. Individual domains/modules are represented by differendy shaded boxes. The known structural features and functions of domains are indicated. The following abbreviations for the different domains were used NLS, nuclear localization sequence TRSEEX, Thr-Arg-Ser-Glu-Glu-Xaa repeat motif Ub, ubiquitin-like domain Bag, Bag homology region WW, Trp-Trp domain TPR, tetratricopeptide repeat GGMP, Gly-Gly-Met-Pro repeat motif +/—, charged region U box, U box motif of E4 ubiquitin ligases DnaK, interaction site for DnaK 70, interaction site for Hsp70 90, interaction site for Hsp90.

The a-subunits display sequence homology of 25-45%, but their seconda and tertiary structures are highly conserved. They all possess the same pattern of residues, a repeated (3 or 4 times) divalent cation-binding motif, and a relatively well conserved transmembrane domain. 

---