Fig. 3.

TβR-I alone adopts a similar overall secondary structure and cis-prolyl peptide bond compared to the bound form. (a) Secondary structural probabilities for the unbound form of TβR-I, deduced on the basis of secondary shifts using the program PECAN,²⁴ correlate closely with secondary structures for the TGF-β1-bound and TGF-β3-bound forms of TβR-I (PDB codes: 3KFD and 2PJY, respectively). Secondary structures were calculated from the structures of the bound forms using the program DSSP.²⁵ (b) cis-Xaa-Pro and trans-Xaa-Pro peptide bonds are characterized by close interproton distances between Xaa H^α and either Pro H^α or Pro H^δ1/H^δ2, respectively.²⁶ (c) Strips from a 3D ¹³C-edited NOESY spectrum from the C^α/H^α positions of Ile54 H^α, Pro55 H^α, Pro55 H^δ1, and Pro55 H ^δ2. NOEs between Ile54 H^α and Pro55 H^α indicative of a cis peptide bond are identified by broken lines. Positive and negative signals are drawn with black and red contours, respectively.