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Backbone dynamics measurements on leukemia inhibitory factor, a rigid four‐helical bundle cytokine
Author(s) -
Yao Shenggen,
Smith David K.,
Hinds Mark G.,
Zhang JianGuo,
Nicola Nicos A.,
Norton Raymond S.
Publication year - 2000
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.9.4.671
Subject(s) - chemistry , molecular dynamics , crystallography , anisotropy , relaxation (psychology) , computational chemistry , physics , psychology , social psychology , quantum mechanics
Abstract The backbone dynamics of the four‐helical bundle cytokine leukemia inhibitory factor (LIF) have been investigated using 15 N NMR relaxation and amide proton exchange measurements on a murine—human chimera, MH35‐LIF. For rapid backbone motions (on a time scale of 10 ps to 100 ns), as probed by 15 N relaxation measurements, the dynamics parameters were calculated using the model‐free formalism incorporating the model selection approach. The principal components of the inertia tensor of MH35‐LIF, as calculated from its NMR structure, were 1:0.98:0.38. The global rotational motion of the molecule was, therefore, assumed to be axially symmetric in the analysis of its relaxation data. This yielded a diffusion anisotropy D ⟂ D ⟂ of 1.31 and an effective correlation time (4 D ⟂ + 2D ⟂ ) −1 of 8.9 ns. The average values of the order parameters ( S 2 ) for the four helices, the long interhelical loops, and the N‐terminus were 0.91, 0.84, and 0.65, respectively, indicating that LIF is fairly rigid in solution, except at the N‐terminus. The S 2 values for the long interhelical loops of MH35‐LIF were higher than those of their counterparts in short‐chain members of the four‐helical bundle cytokine family. Residues involved in LIF receptor binding showed no consistent pattern of backbone mobilities, with S 2 values ranging from 0.71 to 0.95, but residues contributing to receptor binding site III had relatively lower S 2 values, implying higher amplitude motions than for the backbone of sites I and II. In the relatively slow motion regime, backbone amide exchange measurements showed that a number of amides from the helical bundle exchanged extremely slowly, persisting for several months in 2 H 2 O at 37 °C. Evidence for local unfolding was considered, and correlations among various structure‐related parameters and the backbone amide exchange rates were examined. Both sets of data concur in showing that LIF is one of the most rigid four‐helical bundle cytokines.