Figure 4

NMR ensemble scanning results for PDB structure 2B1O. 2B1O is a structure of a protein which is known to bind calcium (Ca²⁺). The NMR ensemble for 2B1O contains different conformations of the structure, some of which show different proclivities for binding Ca²⁺. A shows 10 NMR generated structures for one of the known Ca²⁺ binding loops, superimposed to minimize RMSD; B shows loops that FEATURE does not identify as Ca²⁺ binding, corresponding to NMR models 1, 3, 4, 5, 6, and 10; and C shows loops that FEATURE does identify as Ca²⁺ binding, corresponding to NMR models 2, 7, 8, and 9. In B and C, sidechains in the vicinity of the FEATURE hits are shown for the highest scoring NMR model (score ~39 for B and ~64 for C). In C, one of the hits that scored over the model threshold of 50 is shown as a yellow ball. Notice the differences in the conformations between side chains in B and C: the entire loop is wider in C, and coordinating oxygens form a ring around the hit, while in B they are more scattered. There is also a difference in the conformation of phenylalanine ring, which essentially blocks the Ca²⁺ binding spot in B but is rotated away from the site to allow possible Ca²⁺ binding in C.