Fig. 4

Syncrip N-terminal and extended RRM1 domains are coupled by a specific and dynamic interface. a Cartoon representation of the structure of Syncrip N-terminal region (NeR1). The side chains of the amino acids mediating the inter-domain interaction are displayed as sticks and coloured in green (N-terminal domain), yellow (αββ extension) and blue (RRM core domain). b Schematic of the inter-domain contacts using the same colour coding as in panel a. Dashed lines represent the interactions between residues. Hydrophobic interactions are in black, hydrogen bonds in red. c Conservation of the inter-domain interface. Residues conserved in Drosophila and human are coloured in red (identical) or orange (same residue type). d Amide resonances of either domain that change in the context of two-domain construct are coloured in purple on the NeR1 structure. The changes observed are limited to the interaction surface observed in the crystal, indicating that the conformation observed in the X-ray structure represents the major conformer in solution. e Heteronuclear NOE and f rotational correlation time (τ_c) values mapped along the protein’s sequence. The secondary structure is drawn at the bottom of each panel. The trend of NOE and τ_c values along the sequence indicates that two domains are stably folded while amino acids in the inter-domain linker (grey background) and in the loop between the canonical fold and αββ extension of the RRM are more flexible. The different τ_c values indicates that the two domains do not tumble together. g Correlation between experimentally measured RDCs, and RDCs back-calculated from the crystal structure using the programme Module. In the left-hand panel a single tensor was used to fit the data, while in the right-hand panel two tensors corresponding to the two domains (green: N-terminal domain blue: extended RRM1) were used in the fit. The two-tensor fit shows a much better correlation with the data (the correlation coefficient between measured and calculated RDCs was 0.914 instead of 0.363) confirming that the two domains do not behave as a single stable structural unit in solution