Interactions between PTB RRMs Induce Slow Motions and Increase RNA Binding Affinity

JOURNAL OF MOLECULAR BIOLOGY

卷:397

Article

Maynard, Caroline M.¹  Hall, Kathleen B.¹ 

[1] Washington Univ, Sch Med, Dept Biochem & Mol Biophys, St Louis, MO 63110 USA

关键词: polypyrimidine tract binding protein;    RRM;    15N relaxation;    protein dynamics;    RNA binding;   

DOI  :  10.1016/j.jmb.2009.12.051

来源: Elsevier

【 摘 要 】

Polypyrimidine tract binding protein (PTB) participates in a variety of functions in eukaryotic cells, including alternative splicing, mRNA stabilization, and internal ribosomal entry site-mediated translation initiation. Its mechanism of RNA recognition is determined in part by the novel geometry of its two C-terminal RNA recognition motifs (RRM3 and RRM4), which interact with each other to form a stable complex (PTB1:34). This complex itself is unusual among RRMs, suggesting that it performs a specific function for the protein. In order to understand the advantage it provides to PTB, the fundamental properties of PTB1:34 are examined here as a comparative study of the complex and its two constituent RRMs. Both RRM3 and RRM4 adopt folded structures that NMR data show to be similar to their structure in PRB1:34. The RNA binding properties of the domains differ dramatically. The affinity of each separate RRM for polypyrimidine tracts is far weaker than that of PTB1:34, and simply mixing the two RRMs does not create an equivalent binding platform. N-15 NMR relaxation experiments show that PTB1:34 has slow, microsecond motions throughout both RRMs including the interdomain linker. This is in contrast to the individual domains, RRM3 and RRM4, where only a few backbone amides are flexible on this time scale. The slow backbone dynamics of PTB1:34, induced by packing of RRM3 and RRM4, could be essential for high-affinity binding to a flexible polypyrimidine tract RNA and also provide entropic compensation for its own formation. (C) 2009 Elsevier Ltd All rights reserved.

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