title: Phosphorylation of phosducin accelerates rod recovery from transducin translocation.
abstract: OBJECTIVE
  In rods saturated by light, the G protein transducin undergoes translocation from the outer segment compartment, which results in the uncoupling of transducin from its innate receptor, rhodopsin. We measured the kinetics of recovery from this adaptive cellular response, while also investigating the role of phosducin, a phosphoprotein binding transducin βγ subunits in its de-phosphorylated state, in regulating this process.
  
  
  METHODS
  Mice were exposed to a moderate rod-saturating light triggering transducin translocation, and then allowed to recover in the dark while free running. The kinetics of the return of the transducin subunits to the outer segments were compared in transgenic mouse models expressing full-length phosducin, and phosducin lacking phosphorylation sites serine 54 and 71, using Western blot analysis of serial tangential sections of the retina.
  
  
  RESULTS
  In mice expressing normal phosducin, transducin α and βγ subunits returned to the outer segments with a half-time (t(1/2)) of ∼24 and 29 minutes, respectively. In the phosducin phosphorylation mutants, the transducin α subunit moved four times slower, with t(1/2) ∼95 minutes, while the movement of transducin βγ was less affected.
  
  
  CONCLUSIONS
  We demonstrate that the recovery of rod photoreceptors from the ambient saturating levels of illumination, in terms of the return of the light-dispersed transducin subunits to the rod outer segments, occurs six times faster than reported previously. Our data also support the notion that the accumulation of transducin α subunit in the outer segment is driven by its re-binding to the transducin βγ dimer, because this process is accelerated significantly by phosducin phosphorylation.
authors.affiliation: Department of Ophthalmology, West Virginia University, Morgantown, West Virginia, USA.
authors.forename: Marycharmain
authors.initials: M
authors.lastname: Belcastro
authors.forename: Hongman
authors.initials: H
authors.lastname: Song
authors.forename: Satyabrata
authors.initials: S
authors.lastname: Sinha
authors.forename: Chunyan
authors.initials: C
authors.lastname: Song
authors.forename: Peter H
authors.initials: PH
authors.lastname: Mathers
authors.forename: Maxim
authors.initials: M
authors.lastname: Sokolov
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003623:Dark Adaptation; D005136:Eye Proteins / Q000378:metabolism*; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D020555:GTP-Binding Protein Regulators / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism*; D006207:Half-Life; D008027:Light; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport / Q000528:radiation effects; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism* / Q000528:radiation effects; D012243:Rhodopsin / Q000378:metabolism; D015293:Transducin / Q000378:metabolism*
chemical_list: D005136:Eye Proteins; D020555:GTP-Binding Protein Regulators; D044385:GTP-Binding Protein alpha Subunits; C488949:Gnat1 protein, mouse; D010750:Phosphoproteins; D021122:Protein Subunits; C065631:phosducin; D012243:Rhodopsin; D015293:Transducin