Accurate Molecular Decision Making during Protein Biogenesis

California Institute Of Technology, Pasadena CA

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Abstract

Project Summary: Accurate Molecular Decision Making during Protein Biogenesis Accurate protein biogenesis is a pre-requisite for the generation and maintenance of a functional proteome and, by extension, for human health. Our long-term goal is to understand the molecular mechanisms by which diverse protein biogenesis pathways in the cell accurately select nascent protein substrates and ensure their correct folding, localization, maturation, and quality control. Three major components define our research program in the next grant cycle. Firstly, we will define how nascent proteins acquire the correct set of chemical modifications during translation, which play essential roles in the maturation, localization, and stability of the proteome. These studies will include N-terminal methionine excision by methionine aminopeptidases, protein acetylation by multiple classes of N-acetyltransferases, and protein acylation by N-terminal myristoyltransferases. In addition to establishing the cotranslational mechanisms of these essential enzymes for the first time, these enzymes will provide a case study for how diverse protein biogenesis machineries gain timely and selective access to the nascent proteome in the crowded environment of the ribosome exit site. Secondly, we will decipher how cotranslational chaperones guide nascent proteins through the most productive biogenesis pathways. We will focus on two goals: (i) Test the role of the nascent polypeptide-associated complex (NAC) as a master regulator of diverse cotranslational protein biogenesis machineries; and (ii) Decipher the mechanism by which the ribosome- associated complex (RAC) together with Hsp70 facilitate cotranslational protein folding. These studies will establish a new model to understand the spatiotemporal coordination of diverse protein biogenesis pathways at the ribosome and probe the mechanisms by which the Hsp70 machinery cooperates with the translating ribosome to reshape the folding trajectory of nascent proteins. Thirdly, we will probe the mechanism of mitochondrial biogenesis and protein quality control. We will use selective ribosome profiling to uncover and understand cotranslational protein targeting to mitochondria. We will decipher the molecular mechanism of the recently discovered AAA+ chaperone Skd3, which displays multiple distinct chaperone activities that may be particularly suited to its role as the only general chaperone in the mitochondrial intermembrane space (IMS). These studies will address long-standing questions about protein targeting to mitochondria and protein folding in the mitochondrial IMS and provide insights into the molecular principles governing these processes. The proposed research will not only generate high-resolution understandings of many protein biogenesis pathways, but also establish valuable conceptual frameworks to understand how nascent proteins are accurately selected into their appropriate biogenesis pathways in the crowded cytosolic environment.