title: Oligomerization with wt αA- and αB-crystallins reduces proteasome-mediated degradation of C-terminally truncated αA-crystallin.
abstract: OBJECTIVE
  We previously demonstrated that the ubiquitin-proteasome pathway (UPP) is a general protein quality control system that selectively degrades damaged or abnormal lens proteins, including C-terminally truncated αA-crystallin. The objective of this work was to determine the effects of wt αA- and αB-crystallins on the degradation of C-terminally truncated αA-crystallin (αA(1-162)) and vice versa.
  
  
  METHODS
  Recombinant wt αA, αB, and αA(1-162) were expressed in Escherichia coli and purified to homogeneity by chromatography. Subunit exchange and oligomerization were detected by fluorescence resonance energy transfer (FRET), multiangle-light scattering and coprecipitation assays. Protein substrates were labeled with (125)I and lens epithelial cell lysates were used as the source of the UPP for degradation assays.
  
  
  RESULTS
  FRET, multiangle light scattering, and coprecipitation assays showed that αA(1-162) exchanged subunits with wt αA- or wt αB- crystallin to form hetero-oligomers. αA(1-162) was more susceptible than wt αA-crystallin to degradation by the UPP. When mixed with wt αA-crystallin at 1:1 or 1:4 (αA(1-162) : wt) ratios to form hetero-oligomers, the degradation of αA(1-162) was significantly decreased. Conversely, formation of hetero-oligomers with αA(1-162) enhanced the degradation of wt αA-crystallin. The presence of αA(1-162), but not wt αA-crystallin, decreased the degradation of wt αB-crystallin.
  
  
  CONCLUSIONS
  αA(1-162) forms hetero-oligomers with wt αA- and αB-crystallins. Oligomerization with wt αA- or αB-crystallins reduces the susceptibility of αA(1-162) to degradation by the UPP. In addition, the presence of αA(1-162) in the hetero-oligomers also affects the degradation of wt αA- and αB-crystallins.
authors.affiliation: Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington Street, Boston, MA 02111, USA. wumingx@mail.sysu.edu.cn
authors.forename: Mingxing
authors.initials: M
authors.lastname: Wu
authors.forename: Xinyu
authors.initials: X
authors.lastname: Zhang
authors.forename: Qingning
authors.initials: Q
authors.lastname: Bian
authors.forename: Allen
authors.initials: A
authors.lastname: Taylor
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Liang
authors.forename: Linlin
authors.initials: L
authors.lastname: Ding
authors.forename: Joseph
authors.initials: J
authors.lastname: Horwitz
authors.forename: Fu
authors.initials: F
authors.lastname: Shang
mesh_terms: D002478:Cells, Cultured; D004847:Epithelial Cells; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes; D006801:Humans; D007908:Lens, Crystalline; D008027:Light; D046988:Proteasome Endopeptidase Complex / Q000502:physiology*; D059748:Proteolysis; D012542:Scattering, Radiation; D038202:alpha-Crystallin A Chain / Q000737:chemistry* / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D038202:alpha-Crystallin A Chain; D038203:alpha-Crystallin B Chain; D046988:Proteasome Endopeptidase Complex