TY - JOUR
T1 - Interactions between PTB RRMs Induce Slow Motions and Increase RNA Binding Affinity
AU - Maynard, Caroline M.
AU - Hall, Kathleen B.
N1 - Funding Information:
We thank Dr Greg DeKoster for his NMR advice and assistance. This work is supported by NIH grant GM077231 to K.B.H. C.M.M. was supported in part by NIH grant T32 GM008492 and by a Sigma-Cori predoctoral fellowship.
PY - 2010/3/19
Y1 - 2010/3/19
N2 - 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. 15N 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.
AB - 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. 15N 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.
KW - 15N relaxation
KW - RNA binding
KW - RRM
KW - polypyrimidine tract binding protein
KW - protein dynamics
UR - http://www.scopus.com/inward/record.url?scp=77249156731&partnerID=8YFLogxK
U2 - 10.1016/j.jmb.2009.12.051
DO - 10.1016/j.jmb.2009.12.051
M3 - Article
C2 - 20080103
AN - SCOPUS:77249156731
SN - 0022-2836
VL - 397
SP - 260
EP - 277
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 1
ER -