RESUMO
The Golgi complex is an essential organelle of the eukaryotic exocytic pathway. A subfamily of Golgi matrix proteins, called GRASPs, is central in stress-induced unconventional secretion, Golgi dynamics during mitosis/apoptosis, and Golgi ribbon formation. The Golgi ribbon is vertebrate-specific and correlates with the appearance of two GRASP paralogues and two Golgins (GM130/Golgin45), which form specific GRASP-Golgin pairs. The molecular details of their appearance only in Metazoans are unknown. Moreover, despite new functionalities supported by GRASP paralogy, little is known about their structural and evolutionary differences. Here, we used ancestor sequence reconstruction and biophysical/biochemical approaches to assess the evolution of GRASPs structure/dynamics, fibrillation, and how they started anchoring their Golgin partners. Our data showed that a GRASP ancestor anchored Golgins before gorasp gene duplication in Metazoans. After gene duplication, variations within the GRASP binding pocket determined which paralogue would recruit which Golgin. These interactions are responsible for their specific Golgi location and Golgi ribbon appearance. We also suggest that GRASPs have a long-standing capacity to form supramolecular structures, affecting their participation in stress-induced processes.
Assuntos
Complexo de Golgi/fisiologia , Proteínas da Matriz do Complexo de Golgi/metabolismo , Estresse Fisiológico , Sequência de Aminoácidos , Proteínas da Matriz do Complexo de Golgi/química , Proteínas da Matriz do Complexo de Golgi/genética , Interações Hidrofóbicas e Hidrofílicas , Modelos Moleculares , Filogenia , Ligação Proteica , Conformação Proteica , Transporte Proteico , Relação Estrutura-Atividade , TermodinâmicaRESUMO
GRASP55 is a myristoylated protein localized in the medial/trans-Golgi faces and involved in the Golgi structure maintenance and the regulation of unconventional secretion pathways. It is believed that GRASP55 achieves its main functionalities in the Golgi organization by acting as a tethering factor. When bound to the lipid bilayer, its orientation relative to the membrane surface is restricted to determine its proper trans-oligomerization. Despite the paramount role of myristoylation in GRASP function, the impact of such protein modification on the membrane-anchoring properties and the structural organization of GRASP remains elusive. Here, an optimized protocol for the myristoylation in E. coli of the membrane-anchoring domain of GRASP55 is presented. The biophysical properties of the myristoylated/non-myristoylated GRASP55 GRASP domain were characterized in a membrane-mimicking micellar environment. Although myristoylation did not cause any impact on the protein's secondary structure, according to our circular dichroism data, it had a significant impact on the protein's thermal stability and solubility. Electrophoresis of negatively charged liposomes incubated with the two GRASP55 constructions showed different electrophoretic mobility for the myristoylated anchored protein only, thus demonstrating that myristoylation is essential for the biological membrane anchoring. Molecular dynamics simulations were used to further explore the anchoring process in determining the restricted orientation of GRASPs in the membrane.
Assuntos
Escherichia coli , Proteínas de Membrana , Escherichia coli/metabolismo , Complexo de Golgi/metabolismo , Proteínas da Matriz do Complexo de Golgi/metabolismo , Humanos , Bicamadas Lipídicas/metabolismo , Proteínas de Membrana/químicaRESUMO
Human respiratory syncytial virus (HRSV) envelope glycoproteins traffic to assembly sites through the secretory pathway, while nonglycosylated proteins M and N are present in HRSV inclusion bodies but must reach the plasma membrane, where HRSV assembly happens. Little is known about how nonglycosylated HRSV proteins reach assembly sites. Here, we show that HRSV M and N proteins partially colocalize with the Golgi marker giantin, and the glycosylated F and nonglycosylated N proteins are closely located in the trans-Golgi, suggesting their interaction in that compartment. Brefeldin A compromised the trafficking of HRSV F and N proteins and inclusion body sizes, indicating that the Golgi is important for both glycosylated and nonglycosylated HRSV protein traffic. HRSV N and M proteins colocalized and interacted with sorting nexin 2 (SNX2), a retromer component that shapes endosomes in tubular structures. Glycosylated F and nonglycosylated N HRSV proteins are detected in SNX2-laden aggregates with intracellular filaments projecting from their outer surfaces, and VPS26, another retromer component, was also found in inclusion bodies and filament-shaped structures. Similar to SNX2, TGN46 also colocalized with HRSV M and N proteins in filamentous structures at the plasma membrane. Cell fractionation showed enrichment of SNX2 in fractions containing HRSV M and N proteins. Silencing of SNX1 and 2 was associated with reduction in viral proteins, HRSV inclusion body size, syncytium formation, and progeny production. The results indicate that HRSV structural proteins M and N are in the secretory pathway, and SNX2 plays an important role in the traffic of HRSV structural proteins toward assembly sites.IMPORTANCE The present study contributes new knowledge to understand HRSV assembly by providing evidence that nonglycosylated structural proteins M and N interact with elements of the secretory pathway, shedding light on their intracellular traffic. To the best of our knowledge, the present contribution is important given the scarcity of studies about the traffic of HRSV nonglycosylated proteins, especially by pointing to the involvement of SNX2, a retromer component, in the HRSV assembly process.
Assuntos
Precursor de Proteína beta-Amiloide/metabolismo , Interações entre Hospedeiro e Microrganismos , Proteínas do Nucleocapsídeo/metabolismo , Vírus Sincicial Respiratório Humano/fisiologia , Proteínas Virais/metabolismo , Montagem de Vírus , Precursor de Proteína beta-Amiloide/genética , Proteínas de Transporte , Complexo de Golgi/metabolismo , Proteínas da Matriz do Complexo de Golgi/metabolismo , Células HeLa , Humanos , Transporte ProteicoRESUMO
The Golgi complex is a central component of the secretory pathway, responsible for several critical cellular functions in eukaryotes. The complex is organized by the Golgi matrix that includes the Golgi reassembly and stacking protein (GRASP), which was shown to be involved in cisternae stacking and lateral linkage in metazoan. GRASPs also have critical roles in other processes, with an unusual ability to interact with several different binding partners. The conserved N terminus of the GRASP family includes two PSD-95, DLG, and ZO-1 (PDZ) domains. Previous crystallographic studies of orthologues suggest that PDZ1 and PDZ2 have similar conformations and secondary structure content. However, PDZ1 alone mediates nearly all interactions between GRASPs and their partners. In this work, NMR, synchrotron radiation CD, and molecular dynamics (MD) were used to examine the structure, flexibility, and stability of the two constituent PDZ domains. GRASP PDZs are structured in an unusual ß3 α1 ß4 ß5 α2 ß6 ß1 ß2 secondary structural arrangement and NMR data indicate that the PDZ1 binding pocket is formed by a stable ß2 -strand and a more flexible and unstable α2 -helix, suggesting an explanation for the higher PDZ1 promiscuity. The conformational free energy profiles of the two PDZ domains were calculated using MD simulations. The data suggest that, after binding, the protein partner significantly reduces the conformational space that GRASPs can access by stabilizing one particular conformation, in a partner-dependent fashion. The structural flexibility of PDZ1, modulated by PDZ2, and the coupled, coordinated movement between the two PDZs enable GRASPs to interact with multiple partners, allowing them to function as promiscuous, multitasking proteins.
Assuntos
Proteínas da Matriz do Complexo de Golgi/química , Proteínas da Matriz do Complexo de Golgi/metabolismo , Domínios PDZ , Conformação Proteica , Sequência de Aminoácidos , Cristalografia por Raios X , Humanos , Simulação de Dinâmica Molecular , Ligação Proteica , Homologia de SequênciaRESUMO
In mammals, the Golgi apparatus is the central hub for intracellular trafficking, sorting and post-translational modifications of proteins and lipids. Golgi reassembly and stacking proteins (GRASPs) are somehow involved in Golgi stacking, which is relevant for its proper function, and also in unconventional protein secretion. However, the structural details on how GRASPs accomplish those tasks are still elusive. Here, we have explored the biochemical and biophysical properties of human full-length GRASP55 in solution. Sequence-based analyses and circular dichroism spectroscopy suggest that GRASP55 presents multiple intrinsically disordered sites, although keeping considerable contents of regular secondary structure. Size exclusion chromatography and multiple-angle light scattering show that GRASP55 are monomers in solution. Urea denaturation of GRASP55 suggests the transition to the unfolded state is a cooperative process. Differential scanning calorimetry analysis displays two endothermic transitions for GRASP55, indicating the existence of an intermediate state prior to unfolding. Thioflavin T fluorescence suggests GRASP55 intermediate can be aggregates/fibrils. Transmission electron microscopy and fluorescence lifetime imaging microscopy prove GRASP55 forms large amorphous aggregates but not amyloid-like fibrils in the intermediate state. These results could be helpful in discussing the proper function of human GRASP55 in the Golgi organization as well as unconventional secretion of proteins.
Assuntos
Proteínas da Matriz do Complexo de Golgi/química , Complexo de Golgi/metabolismo , Proteínas da Matriz do Complexo de Golgi/metabolismo , Humanos , Desdobramento de Proteína , Soluções , TemperaturaRESUMO
The Golgi complex is part of the endomembrane system and is responsible for receiving transport cargos from the endoplasmic reticulum and for sorting and targeting them to their final destination. To perform its function in higher eukaryotic cells, the Golgi needs to be correctly assembled as a flattened membrane sandwich kept together by a protein matrix. The precise mechanism controlling the Golgi cisternae assembly is not yet known, but it is widely accepted that the Golgi Reassembly and Stacking Protein (GRASP) is a main component of the Golgi protein matrix. Unlike mammalian cells, which have two GRASP genes, lower eukaryotes present only one gene and distinct Golgi cisternae assembly. In this study, we performed a set of biophysical studies to get insights on the structural properties of the GRASP domains (DGRASPs) from both human GRASP55 and GRASP65 and compare them with GRASP domains from lower eukaryotes (Saccharomyces cerevisiae and Cryptococcus neoformans). Our data suggest that both human DGRASPs are essentially different from each other and that DGRASP65 is more similar to the subgroup of DGRASPs from lower eukaryotes in terms of its biophysical properties. GRASP55 is present mainly in the Golgi medial and trans faces, which are absent in both fungi, while GRASP65 is located in the cis-Golgi. We suggest that the GRASP65 gene is more ancient and that its paralogue GRASP55 might have appeared later in evolution, together with the medial and trans Golgi faces in mammalians.