Janitorial system in red blood cells discovered | August 7, 2017 Issue - Vol. 95 Issue 32 | Chemical & Engineering News
Volume 95 Issue 32 | p. 5 | News of The Week
Issue Date: August 7, 2017

Janitorial system in red blood cells discovered

Enzyme helps trash most of the proteins inside cells that are transforming into red blood cells
Department: Science & Technology
News Channels: Biological SCENE, Biological SCENE
Keywords: biochemistry, red blood cells, degradation, proteostasis
Red blood cells have few proteins other than hemoglobin, thanks to a degradation enzyme called UBE2O.
Credit: Shutterstock
Image of red blood cells.
Red blood cells have few proteins other than hemoglobin, thanks to a degradation enzyme called UBE2O.
Credit: Shutterstock

Red blood cells are a stripped-down version of most other cells: The oxygen-carrying workhorses are packed with hemoglobin and little else. As immature red blood cells called reticulocytes transform into dedicated oxygen carriers, they trash their nucleus, organelles, and most proteins. Two groups of scientists are now reporting that this massive and selective clearance event occurs thanks to a protein degradation pathway involving an enzyme called UBE2O.

A team led by Daniel Finley and Mark D. Fleming at Harvard Medical School report that in the last stages of red blood cell differentiation, UBE2O remodels the proteome inside reticulocytes by tagging the small protein ubiquitin onto protein “trash” to signal for its breakdown, leaving the cell with approximately 98% α- and β-globin, the subunits that join to form hemoglobin (Science 2017, DOI: 10.1126/science.aan0218). Meanwhile, Ramanujan S. Hegde and his team at the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, discovered that in reticulocytes, UBE2O also degrades rogue α-globin proteins that have not formed functional hemoglobin.

In other types of cells, Hegde’s team similarly found that UBE2O helps clear out orphan proteins that have also failed to join multiprotein complexes. The enzyme recognizes the proteins and tags them at many sites with individual ubiquitin molecules to signal for degradation.

This is unlike other ubiquitin-based degradation pathways, which tag proteins for destruction with long chains of ubiquitin molecules, explain Randolph Y. Hampton at the University of California, San Diego, and Catherine Dargemont at Paris Diderot University in an associated commentary (Science 2017, DOI: 10.1126/science.aao1896). “Further understanding of UBE2O and other quality-control pathways might open new therapeutic avenues” they add.

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H L Sam Queen (August 15, 2017 2:13 PM)
Excellent report. Protein turnover is an essential function, allowing us to get rid of old or dysfunctional proteins as we gather together the amino acids required for making new proteins. Interference with this process has been shown to cause a variety of diseases and health conditions. Chronic Kidney Disease offers an example, as it is associated with a rise in the protease inhibitor, Cystatin C, the origin of which has been credited to organophosphate exposure (i.e. pesticides or herbicides). It would be interesting to see in some people with hemoglobin-related anemias if an environmental toxin may be working similarly on the RBC janitorial system to interfere with the normal synthesis of fully operational RBCs. Would hope to interest you into looking into this area of general health concern.

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