[Show abstract][Hide abstract] ABSTRACT: Tissue-specific alternative pre-mRNA splicing is often cooperatively regulated by multiple splicing factors, but the structural basis of cooperative RNA recognition is poorly understood. In Caenorhabditis elegans, ligand binding specificity of fibroblast growth factor receptors (FGFRs) is determined by mutually exclusive alternative splicing of the sole FGFR gene, egl-15. Here we determined the solution structure of a ternary complex of the RNA-recognition motif (RRM) domains from the RBFOX protein ASD-1, SUP-12 and their target RNA from egl-15. The two RRM domains cooperatively interact with the RNA by sandwiching a G base to form the stable complex. Multichromatic fluorescence splicing reporters confirmed the requirement of the G and the juxtaposition of the respective cis elements for effective splicing regulation in vivo. Moreover, we identified a new target for the heterologous complex through an element search, confirming the functional significance of the intermolecular coordination.
[Show abstract][Hide abstract] ABSTRACT: Anaphase-promoting complex or cyclosome (APC/C) is a multisubunit ubiquitin ligase E3 that targets cell-cycle regulators. Cdc20 is required for full activation of APC/C in M phase, and mediates substrate recognition. In vertebrates, Emi2/Erp1/FBXO43 inhibits APC/C-Cdc20, and functions as a cytostatic factor that causes long-term M phase arrest of mature oocytes. In this study, we found that a fragment corresponding to the zinc-binding region (ZBR) domain of Emi2 inhibits cell-cycle progression, and impairs the association of Cdc20 with the APC/C core complex in HEK293T cells. Furthermore, we revealed that the ZBR fragment of Emi2 inhibits in vitro ubiquitin chain elongation catalyzed by the APC/C cullin-RING ligase module, the ANAPC2-ANAPC11 subcomplex, in combination with the ubiquitin chain-initiating E2, E2C/UBE2C/UbcH10. Structural analyses revealed that the Emi2 ZBR domain uses different faces for the two mechanisms. Thus, the double-faced ZBR domain of Emi2 antagonizes the APC/C function by inhibiting both the binding with the coactivator Cdc20 and ubiquitylation mediated by the cullin-RING ligase module and E2C. In addition, the tail region between the ZBR domain and the C-terminal RL residues [the post-ZBR (PZ) region] interacts with the cullin subunit, ANAPC2. In the case of the ZBR fragment of the somatic paralogue of Emi2, Emi1/FBXO5, these inhibitory activities against cell division and ubiquitylation were not observed. Finally, we identified two sets of key residues in the Emi2 ZBR domain that selectively exert each of the dual Emi2-specific modes of APC/C inhibition, by their mutation in the Emi2 ZBR domain and their transplantation into the Emi1 ZBR domain.
[Show abstract][Hide abstract] ABSTRACT: Aggregation of TAR DNA-binding protein 43 (TDP-43) is a pathological signature of amyotrophic lateral sclerosis (ALS). Although accumulating evidence suggests the involvement of RNA recognition motifs (RRMs) in TDP-43 proteinopathy, it remains unclear how native TDP-43 is converted to pathogenic forms. To elucidate the role of homeostasis of RRM1 structure in ALS pathogenesis, conformations of RRM1 under high pressure were monitored by NMR. We first found that RRM1 was prone to aggregation and had three regions showing stable chemical shifts during misfolding. Moreover, mass-spectrometric analysis of aggregated RRM1 revealed that one of the regions was located on protease-resistant β-strands containing two cysteines (C173 and C175), indicating that this region served as a core assembly interface in RRM1 aggregation. Although a fraction of RRM1 aggregates comprised disulfide-bonded oligomers, the substitution of cysteine(s) to serine(s) (C/S) resulted in unexpected acceleration of amyloid fibrils of RRM1 and disulfide-independent aggregate formation of full-length TDP-43. Notably, TDP-43 aggregates with RRM1-C/S required C-terminus, and replicated cytopathologies of ALS, including mislocalization, impaired RNA splicing, ubiquitination, phosphorylation, and motor neuron toxicity. Furthermore, RRM1-C/S accentuated inclusions of familial ALS-linked TDP-43 mutants in C-terminus. The relevance of RRM1-C/S-induced TDP-43 aggregates in ALS pathogenesis was verified by immunolabeling of inclusions of ALS patients and cultured cells overexpressing the RRM1-C/S TDP-43 with antibody targeting a misfolding-relevant regions. Our results indicate that cysteines in RRM1 crucially govern the conformation of TDP-43, and aberrant self-assembly of RRM1 at amyloidogenic regions contributes to pathogenic conversion of TDP-43 in ALS.
Journal of Biological Chemistry 04/2013; · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Molecular interactions between the tumor suppressor p53 and the anti-apoptotic Bcl-2 family proteins play an important role in the transcription-independent apoptosis of p53. The p53 transactivation domain (p53TAD) contains two conserved ϕXXϕϕ motifs (ϕ: a bulky hydrophobic residue, X: any other residue) referred to as p53TAD1 (residues 15-29) and p53TAD2 (residues 39-57). We previously showed that p53TAD1 can act as a binding motif for anti-apoptotic Bcl-2 family proteins. In this study, we have examined interactions of p53TAD2 with the anti-apoptotic Bcl-2 family proteins by using NMR spectroscopy and calculated the structures of Bcl-XL/Bcl-2 in complex with the p53TAD2 peptide. NMR chemical shift perturbation data showed that p53TAD2 peptide universally binds to diverse members of the anti-apoptotic Bcl-2 family independently of p53TAD1 and the binding between p53TAD2 and p53TAD1 to Bcl-XL is competitive. Refined structural models of the Bcl-XL/p53TAD2 and Bcl-2/p53TAD2 complexes showed that the binding sites occupied by p53TAD2 in Bcl-XL and Bcl-2 overlap well with those occupied by pro-apoptotic BH3 peptides. Taken together with the mutagenesis, isothermal titration calorimetry (ITC) and paramagnetic relaxation enhancement (PRE) data, our structural comparison provided the structural basis of p53TAD2-mediated interaction with the anti-apoptotic proteins, revealing that Bcl-XL/Bcl-2, MDM2 and CBP/p300 share remarkably similar modes of binding to the dual p53TAD motifs, p53TAD1 and p53TAD2. In conclusion, our results suggest that the dual-site interaction of p53TAD is a highly conserved mechanism underlying target protein binding in the transcription-dependent and transcription-independent apoptotic pathways of p53.
Journal of Biological Chemistry 01/2013; · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The WWE domain is often identified in proteins associated with ubiquitination or poly-ADP-ribosylation. Structural information about WWE domains has been obtained for the ubiquitination-related proteins, such as Deltex and RNF146, but not yet for the poly-ADP-ribose polymerases (PARPs). Here we determined the solution structures of the WWE domains from PARP11 and PARP14, and compared them with that of the RNF146 WWE domain. NMR perturbation experiments revealed the specific differences in their ADP-ribose recognition modes that correlated with their individual biological activities. The present structural information sheds light on the ADP-ribose recognition modes by the PARP WWE domains.
[Show abstract][Hide abstract] ABSTRACT: 'RNA recognition motifs (RRMs)' are common domain-folds composed of 80-90 amino-acid residues in eukaryotes, and have been identified in many cellular proteins. At first they were known as RNA binding domains. Through discoveries over the past 20 years, however, the RRMs have been shown to exhibit versatile molecular recognition activities and to behave as molecular Lego building blocks to construct biological systems. Novel RNA/protein recognition modes by RRMs are being identified, and more information about the molecular recognition by RRMs is becoming available. These RNA/protein recognition modes are strongly correlated with their biological significance. In this review, we would like to survey the recent progress on these versatile molecular recognition modules.
[Show abstract][Hide abstract] ABSTRACT: Multi-targeting therapy is an emerging strategy of drug discovery to improve therapeutic efficacy, safety and resistance profiles. In this study, we monitored the binding of a potent MDM2 inhibitor Nutlin-3 with anti-apoptotic Bcl-2 family proteins using NMR spectroscopy. Our results showed the universal binding of Nutlin-3 with diverse anti-apoptotic Bcl-2 family proteins. Taken together with the binding data for Nutlin-3 analogs, the structural model of the Bcl-X(L)/Nutlin-3 complex showed that the binding mode of Nutlin-3 resembles that of the Bcl-X(L)/Bcl-2 inhibitors, suggesting the molecular mechanism of transcription-independent mitochondrial apoptosis by Nutlin-3. Finally, our structural comparison provides structural insights into the dual-targeting mechanism of how Nutlin-3 can bind to two different target proteins, MDM2 and anti-apoptotic Bcl-2 family proteins in a similar manner.
Biochemical and Biophysical Research Communications 02/2012; 420(1):48-53. · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: RNA helicase A (RHA) is a highly conserved protein with multifaceted functions in the gene expression of cellular and viral mRNAs. RHA recognizes highly structured nucleotides and catalytically rearranges the various interactions between RNA, DNA, and protein molecules to provide a platform for the ribonucleoprotein complex. We present the first solution structures of the double-stranded RNA-binding domains (dsRBDs), dsRBD1 and dsRBD2, from mouse RHA. We discuss the binding mode of the dsRBDs of RHA, in comparison with the known dsRBD structures in their complexes. Our structural data provide important information for the elucidation of the molecular reassembly mediated by RHA.
Proteins Structure Function and Bioinformatics 02/2012; 80(6):1699-706. · 3.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: RNA helicase A (RHA) is a multifunctional protein that regulates gene expression. RHA has two double-stranded RNA-binding domains (dsRBDs) that serve as modules for highly structured RNA binding and protein–protein interactions. Using the dsRBDs, RHA binds to cellular and viral mRNAs, exports them from the nucleus, and regulates splicing as well as translational initiation. The RHA dsRBDs also reportedly mediate interactions with small RNAs and other dsRBD-containing proteins, and altogether form a processing complex involved in RNA silencing pathways. In addition, the RHA dsRBDs bridge RNA polymerase II with several transcription factors. Here we report the 1H, 13C, and 15N chemical shift assignments of the dsRBDs of RHA. The resonance assignments obtained in this work will contribute to the elucidation of the interactions between RHA and transcriptional or post-transcriptional gene regulators.
[Show abstract][Hide abstract] ABSTRACT: The TAR RNA-binding Protein (TRBP) is a double-stranded RNA (dsRNA)-binding protein, which binds to Dicer and is required for the RNA interference pathway. TRBP consists of three dsRNA-binding domains (dsRBDs). The first and second dsRBDs (dsRBD1 and dsRBD2, respectively) have affinities for dsRNA, whereas the third dsRBD (dsRBD3) binds to Dicer. In this study, we prepared the single domain fragments of human TRBP corresponding to dsRBD1 and dsRBD2 and solved the crystal structure of dsRBD1 and the solution structure of dsRBD2. The two structures contain an α-β-β-β-α fold, which is common to the dsRBDs. The overall structures of dsRBD1 and dsRBD2 are similar to each other, except for a slight shift of the first α helix. The residues involved in dsRNA binding are conserved. We examined the small interfering RNA (siRNA)-binding properties of these dsRBDs by isothermal titration colorimetry measurements. The dsRBD1 and dsRBD2 fragments both bound to siRNA, with dissociation constants of 220 and 113 nM, respectively. In contrast, the full-length TRBP and its fragment with dsRBD1 and dsRBD2 exhibited much smaller dissociation constants (0.24 and 0.25 nM, respectively), indicating that the tandem dsRBDs bind simultaneously to one siRNA molecule. On the other hand, the loop between the first α helix and the first β strand of dsRBD2, but not dsRBD1, has a Trp residue, which forms hydrophobic and cation-π interactions with the surrounding residues. A circular dichroism analysis revealed that the thermal stability of dsRBD2 is higher than that of dsRBD1 and depends on the Trp residue.
Protein Science 11/2010; 20(1):118-30. · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human Transformer2-β (hTra2-β) is an important member of the serine/arginine-rich protein family, and contains one RNA recognition motif (RRM). It controls the alternative splicing of several pre-mRNAs, including those of the calcitonin/calcitonin gene-related peptide (CGRP), the survival motor neuron 1 (SMN1) protein and the tau protein. Accordingly, the RRM of hTra2-β specifically binds to two types of RNA sequences [the CAA and (GAA)(2) sequences]. We determined the solution structure of the hTra2-β RRM (spanning residues Asn110-Thr201), which not only has a canonical RRM fold, but also an unusual alignment of the aromatic amino acids on the β-sheet surface. We then solved the complex structure of the hTra2-β RRM with the (GAA)(2) sequence, and found that the AGAA tetra-nucleotide was specifically recognized through hydrogen-bond formation with several amino acids on the N- and C-terminal extensions, as well as stacking interactions mediated by the unusually aligned aromatic rings on the β-sheet surface. Further NMR experiments revealed that the hTra2-β RRM recognizes the CAA sequence when it is integrated in the stem-loop structure. This study indicates that the hTra2-β RRM recognizes two types of RNA sequences in different RNA binding modes.
Nucleic Acids Research 10/2010; 39(4):1538-53. · 8.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The zinc finger CW (zf-CW) domain is a motif of about 60 residues that is frequently found in proteins involved in epigenetic regulation. Here, we determined the NMR solution structure of the zf-CW domain of the human zf-CW and PWWP domain containing protein 1 (ZCWPW1). The zf-CW domain adopts a new fold in which a zinc ion is coordinated tetrahedrally by four conserved Cys ligand residues. The tertiary structure of the zf-CW domain partially resembles that adopted by the plant homeo domain (PHD) finger bound to the histone tail, suggesting that the zf-CW domain and the PHD finger have similar functions. The solution structure of the complex of the zf-CW domain with the histone H3 tail peptide (1-10) with trimethylated K4 clarified its binding mode. Our structural and biochemical studies have identified the zf-CW domain as a member of the histone modification reader modules for epigenetic regulation.
[Show abstract][Hide abstract] ABSTRACT: The Notch signaling pathway is critical for many developmental processes and requires complex trafficking of both Notch receptor and its ligands, Delta and Serrate. In Drosophila melanogaster, the endocytosis of Delta in the signal-sending cell is essential for Notch receptor activation. The Neuralized protein from D. melanogaster (Neur) is a ubiquitin E3 ligase, which binds to Delta through its first neuralized homology repeat 1 (NHR1) domain and mediates the ubiquitination of Delta for endocytosis. Tom, a Bearded protein family member, inhibits the Neur-mediated endocytosis through interactions with the NHR1 domain. We have identified the domain boundaries of the novel NHR1 domain, using a screening system based on our cell-free protein synthesis method, and demonstrated that the identified Neur NHR1 domain had binding activity to the 20-residue peptide corresponding to motif 2 of Tom by isothermal titration calorimetry experiments. We also determined the solution structure of the Neur NHR1 domain by heteronuclear NMR methods, using a (15)N/(13)C-labeled sample. The Neur NHR1 domain adopts a characteristic beta-sandwich fold, consisting of a concave five-stranded antiparallel beta-sheet and a convex seven-stranded antiparallel beta-sheet. The long loop (L6) between the beta6 and beta7 strands covers the hydrophobic patch on the concave beta-sheet surface, and the Neur NHR1 domain forms a compact globular fold. Intriguingly, in spite of the slight, but distinct, differences in the topology of the secondary structure elements, the structure of the Neur NHR1 domain is quite similar to those of the B30.2/SPRY domains, which are known to mediate specific protein-protein interactions. Further NMR titration experiments of the Neur NHR1 domain with the 20-residue Tom peptide revealed that the resonances originating from the bottom area of the beta-sandwich (the L3, L5, and L11 loops, as well as the tip of the L6 loop) were affected. In addition, a structural comparison of the Neur NHR1 domain with the first NHR domain of the human KIAA1787 protein, which is from another NHR subfamily and does not bind to the 20-residue Tom peptide, suggested the critical amino acid residues for the interactions between the Neur NHR1 domain and the Tom peptide. The present structural study will shed light on the role of the Neur NHR1 domain in the Notch signaling pathway.
Journal of Molecular Biology 09/2009; 393(2):478-95. · 3.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The CUG-binding protein 1 (CUG-BP1) is a member of the CUG-BP1 and ETR-like factors (CELF) family or the Bruno-like family and is involved in the control of splicing, translation and mRNA degradation. Several target RNA sequences of CUG-BP1 have been predicted, such as the CUG triplet repeat, the GU-rich sequences and the AU-rich element of nuclear pre-mRNAs and/or cytoplasmic mRNA. CUG-BP1 has three RNA-recognition motifs (RRMs), among which the third RRM (RRM3) can bind to the target RNAs on its own. In this study, we solved the solution structure of the CUG-BP1 RRM3 by hetero-nuclear NMR spectroscopy. The CUG-BP1 RRM3 exhibited a noncanonical RRM fold, with the four-stranded beta-sheet surface tightly associated with the N-terminal extension. Furthermore, we determined the solution structure of the CUG-BP1 RRM3 in the complex with (UG)(3) RNA, and discovered that the UGU trinucleotide is specifically recognized through extensive stacking interactions and hydrogen bonds within the pocket formed by the beta-sheet surface and the N-terminal extension. This study revealed the unique mechanism that enables the CUG-BP1 RRM3 to discriminate the short RNA segment from other sequences, thus providing the molecular basis for the comprehension of the role of the RRM3s in the CELF/Bruno-like family.
Nucleic Acids Research 07/2009; 37(15):5151-66. · 8.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Using an expression protein library of a hyperthermophilic archaeon, Pyrococcus furiosus, we identified a gene (PF0027) that encodes a protein with heat-stable cyclic nucleotide phosphodiesterase (CPDase) activity. The PF0027 gene encoded a 21-kDa protein and an amino acid sequence that showed approximately 27% identity to that of the 2'-5' tRNA ligase protein, ligT (20 kDa), from Escherichia coli. We found that the purified PF0027 protein possessed GTP-dependent RNA ligase activity and that synthetic tRNA halves bearing 2',3'-cyclic phosphate and 5'-OH termini were substrates for the ligation reaction in vitro. GTP hydrolysis was not required for the reaction, and GTPgammaS enhanced the tRNA ligation activity of PF0027 protein, suggesting that the ligation step is regulated by a novel mechanism. In comparison to the strong CPDase activity of the PF0027 protein, the RNA ligase activity itself was quite weak, and the ligation product was unstable during in vitro reaction. Finally, we used NMR to determine the solution structure of the PF0027 protein and discuss the implications of our results in understanding the role of the PF0027 protein.
[Show abstract][Hide abstract] ABSTRACT: The muscleblind-like (MBNL) proteins 1, 2, and 3, which contain four CCCH zinc finger motifs (ZF1-4), are involved in the differentiation of muscle inclusion by controlling the splicing patterns of several pre-mRNAs. Especially, MBNL1 plays a crucial role in myotonic dystrophy. The CCCH zinc finger is a sequence motif found in many RNA binding proteins and is suggested to play an important role in the recognition of RNA molecules. Here, we solved the solution structures of both tandem zinc finger (TZF) motifs, TZF12 (comprising ZF1 and ZF2) and TZF34 (ZF3 and ZF4), in MBNL2 from Homo sapiens. In TZF12 of MBNL2, ZF1 and ZF2 adopt a similar fold, as reported previously for the CCCH-type zinc fingers in the TIS11d protein. The linker between ZF1 and ZF2 in MBNL2 forms an antiparallel beta-sheet with the N-terminal extension of ZF1. Furthermore, ZF1 and ZF2 in MBNL2 interact with each other through hydrophobic interactions. Consequently, TZF12 forms a single, compact global fold, where ZF1 and ZF2 are approximately symmetrical about the C2 axis. The structure of the second tandem zinc finger (TZF34) in MBNL2 is similar to that of TZF12. This novel three-dimensional structure of the TZF domains in MBNL2 provides a basis for functional studies of the CCCH-type zinc finger motifs in the MBNL protein family.
Protein Science 02/2009; 18(1):80-91. · 2.74 Impact Factor