The N-Terminal Domain of the Drosophila Histone mRNA Binding Protein, SLBP, Is Intrinsically Disordered with Nascent Helical Structure

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• 作者：Roopa Thapar ; Geoffrey A. Mueller ; and William F. Marzluff
• 刊名：Biochemistry
• 出版年：2004
• 出版时间：July 27, 2004
• 年：2004
• 卷：43
• 期：29
• 页码：9390 - 9400
• 全文大小：234K
• 年卷期：v.43,no.29(July 27, 2004)
• ISSN：1520-4995

文摘

Stem-loop binding protein (SLBP) is a 31 kDa protein that is central to the regulation ofhistone mRNAs and is highly conserved in metazoans. In vertebrates, the N-terminal domain of SLBPhas sequence determinants necessary for histone mRNA translation, SLBP degradation, cyclin binding,and histone mRNA import. We have used high-resolution NMR spectroscopy and circular dichroism tocharacterize the structural and dynamic features of this domain of SLBP from Drosophila (dSLBP). Wereport that the N-terminal domain of dSLBP is stably unfolded but has nascent helical structure atphysiological pH and native-like solution conditions. The conformational and dynamic properties of theisolated domain are mimicked in a longer 175-residue region of the N-terminus, as well as in the full-length protein. Complete resonance assignments, secondary structure propensity, and motional propertiesof a 91-residue N-terminal domain (G17-K108) of dSLBP are reported here. The deviation of ¹H^{ages/gifchars/alpha.gif" BORDER=0>}, ¹³C^{ages/gifchars/alpha.gif" BORDER=0>},and ¹³C^{ages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">} chemical shifts from random coil reveals that there are four regions between residues I28-A45,S50-L57, S66-G75, and F91-N96 that have helical propensity. These regions also have small but positiveheteronuclear NOEs, interresidue d_NN NOEs, and small but significant protection from solvent exchange.However the lack of medium- and long-range NOEs in 3D ¹⁵N- and ¹³C-edited spectra, fast amide protonexchange rates (all greater than 1 s^-1), and long ¹⁵N relaxation (T₁, T₂) times suggest that the domainfrom dSLBP does not adopt a well-defined tertiary fold. The backbone residual dipolar couplings (RDCs)for this domain are small and lie close to 0 Hz (±2 Hz) for most residues with no well-defined periodicity.The implications of this unfolded state for the function of dSLBP in regulating histone metabolism arediscussed.