Dynamic filtering by two-dimensional 1H NMR with application to phage lambda repressor.

Flexible regions of proteins play an important role in catalysis, ligand binding, and macromolecular interactions. Because of its enhanced sensitivity to motional narrowing, two-dimensional coupling constant J-correlated 1H NMR may be used to observe these regions selectively. Dynamic filtering is an intrinsic feature of this experiment because cross-peak amplitude decays rapidly as linewidths approach the coupling constant. We demonstrate here the flexibility of the NH2-terminal arm of phage lambda repressor, which is thought to wrap around the double helix in the repressor-operator complex. The assignment of arm resonances is made possible by the construction of mutant repressor genes containing successive NH2-terminal deletions.