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Small GTPases - Ras and Rho01:24

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Three regulatory proteins control their activity:
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Rab proteins constitute the largest family of monomeric GTPases, of which 70 members are present in humans. Rab proteins and their effectors regulate consecutive stages of vesicle transport such as vesicle transport, docking, and fusion to the correct recipient membrane.
Rab proteins switch between a cytosolic, GDP-bound inactive state and a membrane-anchored, GTP-bound active state. By themselves, Rabs show slow rates of GDP/GTP exchange and GTP hydrolysis. Thus, Rab proteins are considered...
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Protein Modifications in the RER01:26

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Modification of secretory and transmembrane proteins entering the rough ER begins in the ER lumen. These modifications aid in protein folding and stabilize the acquired tertiary structure. Protein modifications in the rough ER co-occur at different stages of protein folding.
Broadly, these modifications can be categorized into four main categories — glycosylation, formation of disulfide bonds, assembly of protein subunits, and specific proteolytic cleavages like removal of signal...
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Regulation of Nuclear Protein Sorting01:45

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Nuclear protein sorting regulates nucleus composition and gene expression, crucial for determining the fate of a eukaryotic cell. Hence, the entry and exit of molecules across the nuclear envelope is a tightly controlled process. Nuclear protein sorting can be inhibited by one of the following ways: 1) masking cargo signal sequences, 2) modifying the nuclear receptor's affinity for cargo, 3) controlling the nuclear pore size, 4) retaining the cargo during its transit to the cytosol or the...
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Rab Cascades01:25

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Rab GTPases act in a regulated cascade during membrane fusion, helping the lipid bilayers mix. The Rab family of proteins are active when bound to GTP, and inactive when bound to GDP. Hence, they act as guanine nucleotide-dependent molecular switches. Rab-GTP recognizes and binds to long or short-range tethering proteins to capture the target vesicle. These tethers coordinate with SNAREs on the vesicle and the target membrane to assemble the trans SNARE complex that locks the mixing bilayers.
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Export of Misfolded Proteins out of the ER01:32

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After folding, the ER assesses the quality of secretory and membrane proteins. The correctly folded proteins are cleared by the calnexin cycle for transport to their final destination, while misfolded proteins are held back in the ER lumen. The ER chaperones attempt to unfold and refold the misfolded proteins but sometimes fail to achieve the correct native conformation. Such terminally misfolded proteins are then exported to the cytosol by ER-associated degradation or ERAD pathway for...
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Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
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Las extensiones citosólicas regulan directamente una proteasa romboide mediante la modulación de la puerta de entrada

Rosanna P Baker1, Siniša Urban1

  • 1Howard Hughes Medical Institute, Department of Molecular Biology &Genetics, Johns Hopkins University School of Medicine, Room 507 PCTB, 725 North Wolfe Street, Baltimore, Maryland 21205, USA.

Nature
|May 14, 2015
PubMed
Resumen

Los iones de calcio regulan las proteasas intramembranares, específicamente el romboide-4, mediante el control de la entrada del sustrato. Este descubrimiento ofrece nuevos conocimientos sobre la señalización celular y las funciones de la proteasa relacionadas con la enfermedad.

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Área de la Ciencia:

  • La bioquímica es la bioquímica.
  • Biología Molecular Biología Molecular
  • Biología celular Biología celular.

Sus antecedentes:

  • Las proteasas intramembranares son cruciales para la señalización celular y están implicadas en enfermedades.
  • Los mecanismos de regulación directa de estas enzimas ligadas a la membrana siguen siendo en gran medida desconocidos.

Objetivo del estudio:

  • Investigar la regulación directa de las proteasas intramembranares, centrándose en una proteasa romboide con EF-manos de unión al calcio.
  • Para aclarar el papel del calcio en la actividad de la proteasa romboide y el procesamiento del sustrato.

Principales métodos:

  • Caracterización de una proteasa romboide de unión al calcio (romboide-4) en las células de Drosophila.
  • Purificación y reconstitución del liposoma del romboide-4 para estudiar la proteólisis dependiente del calcio.
  • Análisis de las deleciones y mutaciones de la mano EF en los bucles citoplasmáticos para identificar regiones reguladoras.

Principales resultados:

  • El calcio estimula fuertemente la proteólisis por romboide-4 tanto en los sistemas celulares como en los reconstituidos.
  • Los dominios EF-hand son esenciales para prevenir la proteólisis prematura, mientras que los bucles citoplasmáticos median la estimulación inducida por el calcio.
  • La regulación se produce a través de la entrada del sustrato mediada por el calcio, no por la dimerización o la interacción del sustrato.
  • Los sustratos escindidos fuera de la membrana pierden su capacidad reguladora, lo que sugiere que el gating es específico de la proteólisis intramembrana.

Conclusiones:

  • El substrate gating es un mecanismo de regulación evolucionado para la proteólisis intramembrana, que no es esencial para la propia catálisis.
  • El calcio actúa como un regulador directo de la actividad de la proteasa romboide a través del encierro del sustrato.
  • Estos hallazgos abren nuevas vías para estudiar la función de la proteasa romboide y los insumos regulatorios aguas arriba.