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Related Concept Videos

Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

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The straight or branched structure formation of actin filaments is controlled by nucleating proteins such as the formins and Arp2/3 complex. Formin-mediated assembly results in straight filaments, whereas Arp2/3 protein complex-mediated assembly results in branched actin filaments.
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Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...
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Intermediate filaments are cytoskeletal proteins with higher tensile strength and flexibility than microfilaments and microtubules. Unlike the other two cytoskeletal proteins, intermediate filament formation lacks the enzymatic activity to hydrolyze nucleotides like ATP and GTP to generate energy for polymerization. Therefore, the formation of intermediate filaments is multistep self-assembly. The involvement of any accessory proteins in intermediate filament formation has not yet been...
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Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
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Cytoskeletal filaments are polymeric forms of smaller protein subunits. However, individual cytoskeletal filaments may easily disassemble or associate with other similar filaments to form rigid structures. Microfilaments, made of actin monomers, rely on actin-binding proteins to form bundles and create networks of individual actin filaments. Microtubules rely on microtubule-associated proteins (MAPs) to form sturdy cylindrical structures. However, the proteins involved in forming complex...
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The intermediate filaments are one of three widely studied cytoskeletal filaments. They are so named as their diameter (10 nm) is in between that of microfilaments (7 nm) and the microtubules (25 nm).  These filaments are highly stable and can remain intact when exposed to high salt concentrations and detergents. These filaments are responsible for providing stability and mechanical support to the cells. They also help in cell adhesion and maintaining tissue integrity.
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Disassembly of Intermediate Filaments01:35

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Intermediate filaments (IFs) do not undergo spontaneous disassembly. Enzymes, kinases, and phosphatases add and remove phosphates from specific sites to regulate their disassembly. The IF concentration in the cytoplasm also regulates the disassembly. If the concentration crosses a threshold, it activates the protein kinases in the vicinity, allowing the phosphorylation of IFs.
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Updated: Jul 28, 2025

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Structural basis of human PRPS2 filaments.

Guang-Ming Lu1, Huan-Huan Hu1, Chia-Chun Chang1

  • 1School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.

Cell & Bioscience
|May 29, 2023
PubMed
Summary

Human PRPP synthase 2 (hPRPS2) forms polymers in the presence of ADP, a process crucial for its function. Disrupting this polymerization significantly reduces the enzyme

Keywords:
Allosteric regulationCryo-EMCytoophidiumPRPPPRPShPRPS2

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • 5-phosphate ribose-1-pyrophosphate (PRPP) is a vital metabolite synthesized by PRPP synthase (PRPS).
  • Human PRPS has three isoforms (hPRPS1, hPRPS2, hPRPS3), with hPRPS2 showing distinct regulatory properties and cancer relevance.
  • PRPS proteins can polymerize into cytoophidia, a mechanism linked to protein function.

Purpose of the Study:

  • To investigate the function and polymerization mechanism of human PRPS2 (hPRPS2).
  • To determine the structural basis of hPRPS2 polymerization and its regulation.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was used to solve the polymer structure of hPRPS2.
  • Biochemical assays were performed to assess the catalytic activity of wild-type and mutant hPRPS2.
  • Structural analysis focused on ADP binding and inter-hexamer interactions.

Main Results:

  • The hexameric structure of hPRPS2 was determined at 3.08 Å resolution, revealing polymerization into filaments.
  • ADP binding at both allosteric and catalytic sites promotes hPRPS2 hexamer stacking into polymers.
  • A specific point mutation disrupting inter-hexamer contacts abolished polymerization and significantly decreased catalytic activity.

Conclusions:

  • hPRPS2 polymerization is regulated differently compared to bacterial PRPS (ecPRPS).
  • The study provides structural insights into hPRPS2 regulation through polymerization.
  • Findings highlight the importance of hPRPS2 polymerization for its enzymatic function.