RESUMO
The signal recognition particle (SRP), a protein-RNA complex conserved in all three kingdoms of life, recognizes and transports specific proteins to cellular membranes for insertion or secretion. We describe here the 1.8 angstrom crystal structure of the universal core of the SRP, revealing protein recognition of a distorted RNA minor groove. Nucleotide analog interference mapping demonstrates the biological importance of observed interactions, and genetic results show that this core is functional in vivo. The structure explains why the conserved residues in the protein and RNA are required for SRP assembly and defines a signal sequence recognition surface composed of both protein and RNA.
Assuntos
Proteínas de Bactérias/química , Proteínas de Escherichia coli , RNA Bacteriano/química , Partícula de Reconhecimento de Sinal/química , Sequência de Aminoácidos , Proteínas de Bactérias/metabolismo , Pareamento de Bases , Sítios de Ligação , Membrana Celular/metabolismo , Cristalografia por Raios X , Escherichia coli/química , Escherichia coli/genética , Escherichia coli/metabolismo , Guanosina Trifosfato/metabolismo , Ligação de Hidrogênio , Magnésio/metabolismo , Modelos Moleculares , Dados de Sequência Molecular , Conformação de Ácido Nucleico , Potássio/metabolismo , Ligação Proteica , Conformação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , Partícula de Reconhecimento de Sinal/metabolismo , Transformação Bacteriana , Água/metabolismoRESUMO
Metal ions are essential for the folding and activity of large catalytic RNAs. While divalent metal ions have been directly implicated in RNA tertiary structure formation, the role of monovalent ions has been largely unexplored. Here we report the first specific monovalent metal ion binding site within a catalytic RNA. As seen crystallographically, a potassium ion is coordinated immediately below AA platforms of the Tetrahymena ribozyme P4-P6 domain, including that within the tetraloop receptor. Interference and kinetic experiments demonstrate that potassium ion binding within the tetraloop receptor stabilizes the folding of the P4-P6 domain and enhances the activity of the Azoarcus group I intron. Since a monovalent ion binding site is integral to the tetraloop receptor, a tertiary structural motif that occurs frequently in RNA, monovalent metal ions are likely to participate in the folding and activity of a wide diversity of RNAs.