PROTEIN BACKBONE DYNAMICS REVEALED BY QUASI SPECTRAL DENSITY-FUNCTIONANALYSIS OF AMIDE N-15 NUCLEI

Spectral density functions J(0), J(omega(N)), and J(omega(H)+omega(N)) Of individual amide N-15 nuclei in proteins were approximated by a qu asi spectral density function (QSDF). Using this function, the backbon e dynamics were analyzed for seven protein systems on which data have been published. We defined J(0; omega(N)) as the difference between th e J(0) and the J(omega(N)) values, which describes motions slower than 50 (or 60) MHz, and J(omega(N); omega(H+N)) as the difference between the J(omega(N)) and the J((omega)(H)+omega(N)) values, which describe s motions slower than 450 (or 540) MHz. The QSDF analysis can easily e xtract the J(0; omega(N)) of protein backbones, which have often some relation to biologically relevant reactions. Flexible N-terminal regio ns in eglin c and glucose permease IIA and a loop region in eglin c sh owed smaller values of both the J(0; omega(N)) and the J(omega(N); ome ga(H+N)) as compared with the other regions, indicating increases in m otions faster than nanosecond. The values of the J(0; omega(N)) for th e backbone of the FK506 binding protein showed a large variation in th e apoprotein but fell in a very narrow range after the binding of FK50 6. Characteristic increase or decrease in the values of J(0) and J(ome ga(N)) was observed in two or three residues located between secondary structures.