Studies on the structure and binding properties of the cysteine-rich domain of rat low affinity nerve growth factor receptor (p75NGFR).

The binding domain of p75NGFR contains four "repeats" of a 6-cysteine pattern. To test whether these repeats have any structural or functional independence, each repeat has been separately deleted. In each case, deletion led to the loss of most nerve growth factor (NGF) binding activity. The epitopes of two monoclonal antibodies, MC192 and 271c, could be distinguished, however. Repeat IV was found to be unnecessary for binding MC192, whereas Repeat I was not required for binding 217c. This suggests that either terminal repeat can be removed without loss of native-like structure in the remaining repeats. Trp155 in the fourth repeat forms an essential part of the 217c epitope but is not required for either MC192 or NGF binding. Deletion of the linker region between the membrane-spanning domain and the cysteine-rich domain does not affect the binding of NGF or MC192, and has only a slight, if any, effect on 217c binding. Cyclic permutation of the four repeats failed to yield protein capable of binding NGF or MC192.