Millisecond-timescale motions contribute to the function of the bacterial response regulator protein Spo0F

Protein backbones and side chains display varying degrees of flexibility, w hich allows many slightly different but related conformational substates to occur(1). Such fluctuations are known to differ in both timescale and magn itude, from rotation of methyl groups (nanoseconds) to the flipping of buri ed tyrosine rings (seconds)(2,3), Because many mechanisms for protein funct ion require conformational change, it has been proposed that some of these ground-state fluctuations are related to protein function(4). But exactly w hich aspects of motion are functionally relevant remains to be determined. Only a few examples so far exist where function can be correlated to struct ural fluctuations with known magnitude and timescale(5,6). As part of an in vestigation of the mechanism of action of the Bacillus subtilis response re gulator Spo0F, we have explored the relationship between the motional chara cteristics and protein-protein interactions. Here we use a set of nuclear m agnetic resonance N-15 relaxation measurements to determine the relative ti mescales of Spo0F backbone fluctuations on the picosecond-to-millisecond ti mescale, We show that regions having motion on the millisecond timescale co rrelate with residues and surfaces that are known to be critical for protei n-protein interactions.