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Related Concept Videos

Phosphorylation01:02

Phosphorylation

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The addition or removal of phosphate groups from proteins is the most common chemical modification that regulates cellular processes. These modifications can affect the structure, activity, stability, and localization of proteins within cells as well as their interactions with other proteins.
During phosphorylation, protein kinases transfer the terminal phosphate group of ATP to specific amino acid side chains of substrate proteins. Serine, threonine, and tyrosine are the most commonly...
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Phosphoinositides and PIPs01:42

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Phosphoinositides are a group of phospholipids containing a glycerol backbone with two fatty acid chains and a phosphate attached to a myoinositol sugar ring. The inositol head group extends into the cytoplasm, where it is modified by adding phosphate groups to form phosphatidylinositol phosphates or PIPs.
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ATP-driven pumps, also known as transport ATPases, are integral membrane proteins. They have binding sites for ATP located on the membrane's cytosolic side and the ion-conducting domain in the transmembrane region. These pumps use the free energy released from ATP hydrolysis to move the solutes across cell membranes against an electrochemical gradient.
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Proteins undergo chemical modifications that trigger changes in the charge, structure, and conformation of the proteins. Phosphorylation, acetylation, glycosylation, nitrosylation, ubiquitination, lipidation, methylation, and proteolysis are various protein modifications that regulate protein activity. Such modifications are usually enzyme-driven.
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Polyprotic Acids03:38

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Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
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Resting Membrane Potential01:24

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The relative difference in electrical charge, or voltage, between the inside and the outside of a cell membrane, is called the membrane potential. It is generated by differences in permeability of the membrane to various ions and the concentrations of these ions across the membrane.
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Phosphoproteomic Strategy for Profiling Osmotic Stress Signaling in Arabidopsis
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Phosphosite charge rather than shootward localization determines OCTOPUS activity in root protophloem.

Alice S Breda1, Ora Hazak1, Christian S Hardtke2

  • 1Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland.

Proceedings of the National Academy of Sciences of the United States of America
|June 28, 2017
PubMed
Summary

Plant protein OCTOPUS (OPS) activity is determined by its phosphorylation status at S318, not solely by its polar localization. This finding advances our understanding of plant cell development and protein function.

Keywords:
AmborellaBREVIS RADIXGSK3OCTOPUSsieve element

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Area of Science:

  • Plant Biology
  • Cellular Biology
  • Developmental Biology

Background:

  • Polar cellular localization is crucial for protein function in plants.
  • OCTOPUS (OPS) and BREVIS RADIX (BRX) are plasma membrane-associated proteins in Arabidopsis with distinct polar localizations in root protophloem cells.
  • Mutations in OPS and BRX disrupt protophloem differentiation.

Purpose of the Study:

  • To investigate the genetic interaction between OPS and BRX in protophloem development.
  • To determine the functional importance of OPS structural features, including its polar localization and phosphorylation sites.
  • To elucidate the primary determinants of OPS activity.

Main Methods:

  • Genetic analysis of OPS and BRX mutants in Arabidopsis.
  • Protein engineering to alter OPS phosphorylation sites and localization.
  • Functional complementation assays for mutant phenotypes.

Main Results:

  • OPS and BRX act in parallel pathways, with OPS dosage affecting BRX loss-of-function phenotypes.
  • Conserved OPS structural features, including a BIN2 interaction domain, are not essential for function.
  • Modifying the S318 phosphorylation site significantly impacts OPS activity, with hyperactive variants complementing double mutants.
  • Fusion proteins (BRX-OPS, OPS-BRX) localized rootward still complemented ops mutants effectively.

Conclusions:

  • S318 phosphorylation status is a key determinant of OPS activity, overriding the importance of shootward polar localization.
  • OPS function is ancient and conserved, but its activity can be modulated through specific phosphorylation events.
  • Understanding OPS phosphorylation provides new insights into plant cell polarity and differentiation mechanisms.