RESUMO
The human RNA-editing enzyme adenosine deaminase acting on RNA (ADAR1) carries a unique nuclear localization signal (NLS) that overlaps one of its double-stranded RNA-binding domains (dsRBDs). This dsRBD-NLS is recognized by the nuclear import receptor transportin 1 (Trn1; also called karyopherin-ß2) in an RNA-sensitive manner. Most Trn1 cargos bear a well-characterized proline-tyrosine-NLS, which is missing from the dsRBD-NLS. Here, we report the structure of the dsRBD-NLS, which reveals an unusual dsRBD fold extended by an additional N-terminal α-helix that brings the N- and C-terminal flanking regions in close proximity. We demonstrate experimentally that the atypical ADAR1-NLS is bimodular and is formed by the combination of the two flexible fragments flanking the folded domain. The intervening dsRBD acts only as an RNA-sensing scaffold, allowing the two NLS modules to be properly positioned for interacting with Trn1. We also provide a structural model showing how Trn1 can recognize the dsRBD-NLS and how dsRNA binding can interfere with Trn1 binding.
Assuntos
Adenosina Desaminase/metabolismo , beta Carioferinas/metabolismo , Transporte Ativo do Núcleo Celular , Adenosina Desaminase/química , Adenosina Desaminase/genética , Sequência de Aminoácidos , Substituição de Aminoácidos , Células HeLa , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Sinais de Localização Nuclear/química , Sinais de Localização Nuclear/genética , Sinais de Localização Nuclear/metabolismo , Ressonância Magnética Nuclear Biomolecular , Domínios e Motivos de Interação entre Proteínas , Estrutura Secundária de Proteína , RNA de Cadeia Dupla/metabolismo , Proteínas de Ligação a RNA , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Deleção de Sequência , beta Carioferinas/química , beta Carioferinas/genéticaRESUMO
The double-stranded RNA-binding domain (dsRBD) is a small protein domain found in eukaryotic, prokaryotic and viral proteins, whose central property is to bind to double-stranded RNA (dsRNA). Aside from this major function, recent examples of dsRBDs involved in the regulation of the sub-cellular localization of proteins, suggest that the participation of dsRBDs in nucleocytoplasmic trafficking is likely to represent a widespread auxiliary function of this type of RNA-binding domain. Overall, dsRBDs from proteins involved in many different biological processes have been reported to be implicated in nuclear import and export, as well as cytoplasmic, nuclear and nucleolar retention. Interestingly, the function of dsRBDs in nucleocytoplasmic trafficking is often regulated by their dsRNA-binding capacity, which can either enhance or impair the transport from one compartment to another. Here, we present and discuss the emerging function of dsRBDs in nucleocytoplasmic transport.