Characterization of a N-bromoacetyl-L-thyroxine affinity-labeled 55-kilodalton protein as protein disulfide isomerase in cultured glial cells.
In glial cells, thyroid hormone regulates the polymerization state of the actin cytoskeleton by a mechanism that does not require protein synthesis or the nuclear T3 receptor. Using the affinity label N-bromoacetyl-L-T4, we identified a thyroid hormone-binding protein of 55 kDa (glial-p55) in cultured glial cells that is unique from the type II iodothyronine 5'-deiodinase and which exhibits a T4-dependent shift from a membrane-associated pool to the F-actin cytoskeleton. In a number of other cell types, a 55-kDa thyroid hormone-binding protein has been identified and shown to be a subunit of the enzyme protein disulfide isomerase (PDI). In this study we have characterized glial-p55 and compared it with purified rat hepatic PDI. Glial-p55 appears to be identical to PDI by peptide fragmentation analysis, using multiple methods. The hydrodynamic properties of glial-p55, determined by molecular sieve chromatography and sucrose density centrifugation, showed that this protein has a native molecular mass of 115 kDa, which is in close agreement with that reported for PDI. Like PDI, glial-p55 is an acidic protein with a pI of 4.8 or less. Thus, the 55-kDa thyroid hormone-binding protein in glial cells appears to be PDI.
Safran
M
M
Department of Medicine, University of Massachusetts Medical School, Worcester 01655.
Leonard
J L
JL
D000345:Affinity Labels; D000818:Animals; D001253:Astrocytes / Q000201:enzymology*; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D007535:Isomerases / Q000737:chemistry* / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D008970:Molecular Weight; D010449:Peptide Mapping; D019704:Protein Disulfide-Isomerases; D013974:Thyroxine / Q000031:analogs & derivatives* / Q000737:chemistry
D000345:Affinity Labels; C015042:N-bromoacetylthyroxine; D007535:Isomerases; D019704:Protein Disulfide-Isomerases; D013974:Thyroxine