RESUMO
BRPF1 (bromodomain PHD finger 1) is a core subunit of the MOZ histone acetyltransferase (HAT) complex, critical for normal developmental programs and implicated in acute leukemias. BRPF1 contains a unique assembly of zinc fingers, termed a PZP domain, the physiological role of which remains unclear. Here, we elucidate the structure-function relationship of this novel epigenetic reader and detail the biological and mechanistic consequences of its interaction with nucleosomes. PZP has a globular architecture and forms a 2:1 stoichiometry complex with the nucleosome, bivalently interacting with histone H3 and DNA. This binding impacts the nucleosome dynamics, shifting the DNA unwrapping/rewrapping equilibrium toward the unwrapped state and increasing DNA accessibility. We demonstrate that the DNA-binding function of the BRPF1 PZP domain is required for the MOZ-BRPF1-ING5-hEaf6 HAT complex to be recruited to chromatin and to acetylate nucleosomal histones. Our findings reveal a novel link between chromatin dynamics and MOZ-mediated acetylation.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Cromatina/metabolismo , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Nucleossomos/metabolismo , Domínios e Motivos de Interação entre Proteínas , Acetilação , Proteínas Adaptadoras de Transdução de Sinal/genética , Sequência de Aminoácidos , Cromatina/genética , DNA/química , DNA/metabolismo , Proteínas de Ligação a DNA , Histonas/metabolismo , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Complexos Multiproteicos , Proteínas Nucleares/genética , Nucleossomos/genética , Ligação Proteica , Conformação Proteica , Estabilidade Proteica , Alinhamento de SequênciaRESUMO
Poly [ADP-ribose] polymerase 1 (PARP-1) is a highly abundant chromatin-associated enzyme. It catalyzes the NAD(+)-dependent polymerization of long chains of poly-ADP ribose (PAR) onto itself in response to DNA damage and other cues. More recently, the enzymatic activity of PARP-1 has also been implicated in the regulation of gene expression. The molecular basis for the functional switch from chromatin architectural protein to transcription factor and DNA damage responder, triggered by PARP-1 automodification, is unknown. Here, we show that unmodified PARP-1 engages in at least two high-affinity binding modes with chromatin, one of which does not involve free DNA ends, consistent with its role as a chromatin architectural protein. Automodification reduces PARP-1 affinity for intact chromatin but not for nucleosomes with exposed DNA ends. Automodified (AM) PARP-1 has the ability to sequester histones (both in vitro and in cells) and to assemble nucleosomes efficiently in vitro. This unanticipated nucleosome assembly activity of AM-PARP-1, coupled with the fast turnover of the modification, suggests a model in which DNA damage or transcription events trigger transient histone chaperone activity.
