RESUMO
NO38 is a multidomain protein that belongs to the nucleoplasmin (Np) family. Previous studies have suggested that acidic chaperones such as Np may function as histone-storage platforms. Here, the purification and crystallization of the N-terminal domain of NO38 in two crystal forms is reported. The C2 crystal form diffracts to 1.9 A and contains two pentamers in the asymmetric unit, while the P1 crystals diffract to 1.7 A and contain a non-crystallographic decamer with 522 symmetry. By analogy with Np, the NO38 decamer may represent the active form of this chaperone.
Assuntos
Proteínas Nucleares/química , Proteínas Nucleares/isolamento & purificação , Animais , Sítios de Ligação , Cálcio/química , Nucléolo Celular , Cristalografia por Raios X , DNA Complementar/metabolismo , Dimerização , Magnésio/química , Modelos Moleculares , Nucleofosmina , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Difração de Raios X , Xenopus laevisRESUMO
Xenopus NO38 is an abundant nucleolar chaperone and a member of the nucleoplasmin (Np) family. Here, we report high-resolution crystal structures of the N-terminal domain of NO38, as a pentamer and a decamer. As expected, NO38 shares the Np family fold. In addition, NO38- and Np-core pentamers each use highly conserved residues and numerous waters to form their respective decamers. Further studies show that NO38 and Np each bind equal amounts of the four core histones. However, NO38 prefers the (H3-H4)(2) tetramer, while Np probably prefers H2A-H2B dimers. We also show that NO38 and Np will each bind noncognate histones when the preferred partner is absent. We suggest that these chaperones must form decamers in order to bind histones and differentiate between histone tetramers and dimers. When taken together, these data imply that NO38 may function as a histone chaperone in the nucleolus.
Assuntos
Nucléolo Celular/metabolismo , Histonas/metabolismo , Chaperonas Moleculares/química , Chaperonas Moleculares/metabolismo , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Sequência de Aminoácidos , Animais , Dados de Sequência Molecular , Nucleofosmina , Ligação Proteica/fisiologia , Estrutura Terciária de Proteína , XenopusRESUMO
The nucleoplasmin-like protein from Drosophila (dNLP) functions as a chaperone for core histones and may remodel chromatin in embryos. We now report the crystal structure of a dNLP-core pentamer at 1.5 A resolution. The monomer has an eight-stranded, beta barrel topology that is similar to nucleoplasmin (Np). However, a signature beta hairpin is tucked in along the lateral surface of the dNLP-core pentamer, while it extends outward in the Np-core decamer. Drosophila NLP and Np both assemble histone octamers. This process may require each chaperone to form a decamer, which would create symmetric binding sites for the histones. Conformational differences between dNLP and Np may reflect their different oligomeric states, while a conserved, nonpolar subunit interface may allow conformational plasticity during histone binding.
