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Septins are protein filaments forming the cytoskeleton along with the microtubules, microfilaments, intermediate filaments, and other accessory proteins. In 1971 while studying the cell division cycle in mutant Saccharomyces cerevisiae Harwell et al. first identified the septin-related genes playing a crucial role in yeast cytokinesis. Fluorescence microscopy revealed that these proteins localize at the budding neck as rings. These ring-like proteins were then named Septins by John Pringle, and...
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The organelle-specific signaling sequences direct proteins synthesized in the cytosol to their final destination like ER, mitochondria, peroxisomes, etc. Some of the proteins directed to ER are then trafficked via vesicles to other organelles within the cell or the extracellular environment through the Golgi complex. For example, the rough ER synthesizes soluble proteins for transportation to the lysosomes or secretion out of the cell. It can also synthesize transmembrane proteins that can...
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A quest for cytosolic sequons and their functions.

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|April 2, 2024
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The N-linked sequon (NXS/T) in human proteins has moonlighting functions beyond N-glycosylation, including nucleic acid binding, especially in zinc finger proteins. Sequon occurrence and usage influence protein function and can be engineered.

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Asx turnsMembrane protein topologyN-glycosylationPosttranslational modificationsProtein structure and functionProtein-DNA bindingSequonsTransmembrane domainsZinc finger proteinsβ-turns

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Evolutionary Biology

Background:

  • N-linked sequons (NXS/T) are primarily known for N-glycosylation in secreted and membrane proteins.
  • The functional roles of these sequons in nucleocytosolic proteins are less understood.
  • Moonlighting functions, where a single protein performs multiple roles, are common in cellular processes.

Purpose of the Study:

  • To investigate the moonlighting functions of N-linked sequons in human nucleocytosolic proteins.
  • To compare sequon roles in nucleocytosolic proteins versus membrane/secreted proteins.
  • To explore the relationship between sequon occurrence, protein length, and other post-translational modifications.

Main Methods:

  • Comparative analysis of sequon distribution in nucleocytosolic, membrane, and secreted human proteins.
  • Bioinformatic analysis of sequon occurrence in relation to protein length and other post-translational modifications (PTMs).
  • Identification of specific protein families, such as zinc finger proteins, exhibiting novel sequon functions.

Main Results:

  • Nucleocytosolic sequons (cyto-sequons) participate in nucleic acid binding, particularly in zinc finger proteins, a function distinct from N-glycosylation.
  • Sequon occurrence is generally proportional to protein length.
  • Sequon density and the ratio of NXS to NXT motifs regulate protein function, including both N-glycosylation and nucleic acid binding.
  • Sequon occurrence is inversely correlated with the prevalence of other PTMs like phosphorylation and structural features like transmembrane helices and disulfide bridges.

Conclusions:

  • N-linked sequons exhibit moonlighting functions in human nucleocytosolic proteins, notably in nucleic acid binding.
  • Protein sequence, length, and PTMs collectively influence the functional roles of N-linked sequons.
  • This study provides insights into protein sequence-function relationships and aids future protein design and engineering efforts.