ABSTRACT
As our understanding of the cell interior has grown, we have come to appreciate that most cellular operations are localized, that is, they occur at discrete and identifiable locations or domains. These cellular domains contain enzymes, machines, and other components necessary to carry out and regulate these localized operations. Here, we review these features of one such operation: the localization and translation of mRNAs within subcellular compartments observed across cell types and organisms. We describe the conceptual advantages and the "ingredients" and mechanisms of local translation. We focus on the nature and features of localized mRNAs, how they travel and get localized, and how this process is regulated. We also evaluate our current understanding of protein synthesis machines (ribosomes) and their cadre of regulatory elements, that is, the translation factors.
Subject(s)
Protein Biosynthesis , Ribosomes , Ribosomes/genetics , Ribosomes/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolismABSTRACT
The spike protein (S) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required for cell entry and is the primary focus for vaccine development. In this study, we combined cryo-electron tomography, subtomogram averaging, and molecular dynamics simulations to structurally analyze S in situ. Compared with the recombinant S, the viral S was more heavily glycosylated and occurred mostly in the closed prefusion conformation. We show that the stalk domain of S contains three hinges, giving the head unexpected orientational freedom. We propose that the hinges allow S to scan the host cell surface, shielded from antibodies by an extensive glycan coat. The structure of native S contributes to our understanding of SARS-CoV-2 infection and potentially to the development of safe vaccines.
Subject(s)
Betacoronavirus/chemistry , Molecular Dynamics Simulation , Spike Glycoprotein, Coronavirus/chemistry , Cryoelectron Microscopy , Electron Microscope Tomography , Glycosylation , Humans , Protein Domains , Protein Multimerization , SARS-CoV-2ABSTRACT
The molecular events that direct nuclear pore complex (NPC) assembly toward nuclear envelopes have been conceptualized in two pathways that occur during mitosis or interphase, respectively. In gametes and embryonic cells, NPCs also occur within stacked cytoplasmic membrane sheets, termed annulate lamellae (AL), which serve as NPC storage for early development. The mechanism of NPC biogenesis at cytoplasmic membranes remains unknown. Here, we show that during Drosophila oogenesis, Nucleoporins condense into different precursor granules that interact and progress into NPCs. Nup358 is a key player that condenses into NPC assembly platforms while its mRNA localizes to their surface in a translation-dependent manner. In concert, Microtubule-dependent transport, the small GTPase Ran and nuclear transport receptors regulate NPC biogenesis in oocytes. We delineate a non-canonical NPC assembly mechanism that relies on Nucleoporin condensates and occurs away from the nucleus under conditions of cell cycle arrest.
Subject(s)
Drosophila Proteins/metabolism , Molecular Chaperones/metabolism , Nuclear Pore Complex Proteins/metabolism , Nuclear Pore/metabolism , Oogenesis , Active Transport, Cell Nucleus , Animals , Drosophila Proteins/genetics , Drosophila melanogaster , Female , Microtubules/metabolism , Molecular Chaperones/genetics , Nuclear Pore Complex Proteins/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , ran GTP-Binding Protein/genetics , ran GTP-Binding Protein/metabolismABSTRACT
The faithful assembly of protein complexes in space and time is a hallmark of cellular homeostasis. Complex assembly might be seeded already during translation, if interacting subunits are recruited to the nascent chain. Here, we review recent discoveries suggesting that such cotranslational assembly is a prominent feature throughout the proteome. It might contribute to the efficiency and efficacy of assembly and occurs in coordination rather than competition with chaperones. We discuss how cotranslational assembly structurally contributes to the organizational order of assembly pathways and their surveillance. Taken together, these novel insights suggest that cotranslational assembly is intimately linked with the regulation of protein abundance, stability, and activity, offering an attractive explanation for many cellular phenomena.
