RESUMEN
The area surrounding the tunnel exit of the 60S ribosomal subunit is a hub for proteins involved in maturation and folding of emerging nascent polypeptide chains. How different factors vie for positioning at the tunnel exit in the complex cellular environment is not well understood. We used in vivo site-specific cross-linking to approach this question, focusing on two abundant factors-the nascent chain-associated complex (NAC) and the Hsp70 chaperone system that includes the J-domain protein co-chaperone Zuotin. We found that NAC and Zuotin can cross-link to each other at the ribosome, even when translation initiation is inhibited. Positions yielding NAC-Zuotin cross-links indicate that when both are present the central globular domain of NAC is modestly shifted from the mutually exclusive position observed in cryogenic electron microscopy analysis. Cross-linking results also suggest that, even in NAC's presence, Hsp70 can situate in a manner conducive for productive nascent chain interaction-with the peptide binding site at the tunnel exit and the J-domain of Zuotin appropriately positioned to drive stabilization of nascent chain binding. Overall, our results are consistent with the idea that, in vivo, the NAC and Hsp70 systems can productively position on the ribosome simultaneously.
Asunto(s)
Proteínas HSP70 de Choque Térmico , Ribosomas , Saccharomyces cerevisiae , Sitios de Unión , Proteínas HSP70 de Choque Térmico/genética , Péptidos/química , Biosíntesis de Proteínas , Dominios Proteicos , Ribosomas/metabolismoRESUMEN
Among the six known ironsulfur (FeS) cluster biogenesis machineries that function across all domains of life only one involves a molecular chaperone system. This machinery, called ISC for 'iron sulfur cluster', functions in bacteria and in mitochondria of eukaryotes including humans. The chaperone system - a dedicated J-domain protein co-chaperone termed Hsc20 and its Hsp70 partner - is essential for proper ISC machinery function, interacting with the scaffold protein IscU which serves as a platform for cluster assembly and subsequent transfer onto recipient apo-proteins. Despite many years of research, surprisingly little is known about the specific role(s) that the chaperones play in the ISC machinery. Here we review three non-exclusive scenarios that range from involvement of the chaperones in the cluster transfer to regulation of the cellular levels of IscU itself.
Asunto(s)
Proteínas Hierro-Azufre , Chaperonas Moleculares , Proteínas Hierro-Azufre/metabolismo , Proteínas Hierro-Azufre/genética , Humanos , Chaperonas Moleculares/metabolismo , Chaperonas Moleculares/genética , Proteínas HSP70 de Choque Térmico/metabolismo , Mitocondrias/metabolismo , Proteínas de Escherichia coli/metabolismo , Proteínas de Escherichia coli/genéticaRESUMEN
J-domain proteins (JDPs) are the largest family of chaperones in most organisms, but much of how they function within the network of other chaperones and protein quality control machineries is still an enigma. Here, we report on the latest findings related to JDP functions presented at a dedicated JDP workshop in Gdansk, Poland. The report does not include all (details) of what was shared and discussed at the meeting, because some of these original data have not yet been accepted for publication elsewhere or represented still preliminary observations at the time.