RESUMO
Nuclear export of mRNA is a critical event in mRNA biogenesis. Passage of mature messenger ribonucleoproteins (mRNPs) through nuclear pore complexes (NPCs) is facilitated by the Mex67/Mtr2 heterodimer. At the NPC cytoplasmic face, the DEAD-box RNA helicase Dbp5 remodels mRNPs by removing Mex67/Mtr2. This remodeling process prevents mRNPs from returning to the nucleus, thereby imposing unidirectionality on mRNA export. Biochemical studies show that Gle1 and inositol hexaphosphate (IP6) activate Dbp5's ATPase activity at the cytoplasmic face of NPC, therefore providing critical spatial regulation of mRNP remodeling during directional transport. Recent structural studies on Dbp5 in free form and in complex with its ligands (ADP, AMPPNP/RNA) as well as with cytoplasmic nucleoporin Nup214 reveal that the binding of ADP or AMPPNP/RNA induces large conformational changes of Dbp5, and RNA and NUP214 bind to Dbp5 in a mutually exclusive manner. These structural data combined with complementary functional analysis significantly advance our understanding on the mechanism governing mRNA export albeit some key issues remain elusive.
Assuntos
RNA Helicases DEAD-box/química , RNA Helicases DEAD-box/metabolismo , Proteínas de Transporte Nucleocitoplasmático/química , Proteínas de Transporte Nucleocitoplasmático/metabolismo , Transporte de RNA , RNA Mensageiro/metabolismo , Proteínas de Schizosaccharomyces pombe/química , Proteínas de Schizosaccharomyces pombe/metabolismo , Cristalografia por Raios X , Humanos , Modelos BiológicosRESUMO
The control of messenger RNA (mRNA) translation and degradation is important in regulation of eukaryotic gene expression. In the general and specialized mRNA decay pathways which involve 5(') â3(') decay, decapping is the central step because it is the controlling gate preceding the actual degradation of mRNA and is a site of numerous control inputs. Removal of the cap structure is catalyzed by a decapping holoenzyme composed of the catalytic Dcp2 subunit and the coactivator Dcp1. Decapping is regulated by decapping activators and inhibitors. Recent structural and kinetics studies indicated that Dcp1 and the substrate RNA promote the closed form of the enzyme and the catalytic step of decapping is rate limiting and accelerated by Dcp1. The conformational change between the open and closed decapping enzyme is important for controlling decapping, and regulation of this transition has been proposed to be a checkpoint for determining the fate of mRNAs. Here we summarize the past and recent advances on the structural and functional studies of protein factors involved in regulating mRNA decapping.
Assuntos
Endorribonucleases/química , Endorribonucleases/fisiologia , Células Eucarióticas/metabolismo , Capuzes de RNA/metabolismo , Animais , Endorribonucleases/genética , Endorribonucleases/metabolismo , Inibidores Enzimáticos/química , Inibidores Enzimáticos/metabolismo , Inibidores Enzimáticos/farmacologia , Células Eucarióticas/enzimologia , Humanos , Modelos Biológicos , Modelos Moleculares , Complexos Multienzimáticos/química , Complexos Multienzimáticos/genética , Complexos Multienzimáticos/metabolismo , Complexos Multienzimáticos/fisiologia , Biossíntese de Proteínas/genética , Biossíntese de Proteínas/fisiologia , Relação Estrutura-AtividadeRESUMO
mRNA decay is critical for the regulation of gene expression and the quality control of mRNA. RNA helicases play a key role in eukaryotic mRNA decay. In general, RNA helicases utilize the energy of ATP hydrolysis to remodel RNA or RNA-protein complexes, resulting in the separation of RNA duplex strand and/or displacement of proteins from the RNA molecule in RNP (ribonucleoprotein) complexes. Recently, high-resolution crystal structures of RNA helicases in mRNA decay have contributed a great deal to our understanding of these key molecules. In the present review, we focus on the structural and mechanistic aspects of three RNA helicases, Dhh1, Upf1 and eIF4AIII, that are involved in eukaryotic mRNA decay.
Assuntos
Células Eucarióticas/metabolismo , RNA Helicases/química , RNA Helicases/metabolismo , Estabilidade de RNA/genética , Adenosina Trifosfatases/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Previsões , Humanos , Hidrólise , Modelos Moleculares , Dados de Sequência Molecular , Conformação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , RNA/metabolismo , RNA Helicases/genética , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Ribonucleoproteínas/genética , Ribonucleoproteínas/metabolismo , Eletricidade EstáticaRESUMO
Edc3 is an enhancer of decapping and serves as a scaffold that aggregates mRNA ribonucleoproteins together for P-body formation. Edc3 forms a network of interactions with the components of the mRNA decapping machinery and has a modular domain architecture consisting of an N-terminal Lsm domain, a central FDF domain, and a C-terminal YjeF-N domain. We have determined the crystal structure of the N-terminally truncated human Edc3 at a resolution of 2.2 A. The structure reveals that the YjeF-N domain of Edc3 possesses a divergent Rossmann fold topology that forms a dimer, which is supported by sedimentation velocity and sedimentation equilibrium analysis in solution. The dimerization interface of Edc3 is highly conserved in eukaryotes despite the overall low sequence homology across species. Structure-based site-directed mutagenesis revealed dimerization is required for efficient RNA binding, P-body formation, and likely for regulating the yeast Rps28B mRNA as well, suggesting that the dimeric form of Edc3 is a structural and functional unit in mRNA degradation.