Deletion of Ser-171 causes inactivation, proteasome-mediated degradation and complete deficiency of human transaldolase.
Homozygous deletion of three nucleotides coding for Ser-171 (S171) of TAL-H (human transaldolase) has been identified in a female patient with liver cirrhosis. Accumulation of sedoheptulose 7-phosphate raised the possibility of TAL (transaldolase) deficiency in this patient. In the present study, we show that the mutant TAL-H gene was effectively transcribed into mRNA, whereas no expression of the TALDeltaS171 protein or enzyme activity was detected in TALDeltaS171 fibroblasts or lymphoblasts. Unlike wild-type TAL-H-GST fusion protein (where GST stands for glutathione S-transferase), TALDeltaS171-GST was solubilized only in the presence of detergents, suggesting that deletion of Ser-171 caused conformational changes. Recombinant TALDeltaS171 had no enzymic activity. TALDeltaS171 was effectively translated in vitro using rabbit reticulocyte lysates, indicating that the absence of TAL-H protein in TALDeltaS171 fibroblasts and lymphoblasts may be attributed primarily to rapid degradation. Treatment with cell-permeable proteasome inhibitors led to the accumulation of TALDeltaS171 in whole cell lysates and cytosolic extracts of patient lymphoblasts, suggesting that deletion of Ser-171 led to rapid degradation by the proteasome. Although the TALDeltaS171 protein became readily detectable in proteasome inhibitor-treated cells, it displayed no appreciable enzymic activity. The results suggest that deletion of Ser-171 leads to inactivation and proteasome-mediated degradation of TAL-H. Since TAL-H is a regulator of apoptosis signal processing, complete deficiency of TAL-H may be relevant for the pathogenesis of liver cirrhosis.
Grossman
Craig E
CE
Department of Medicine, State University of New York UMU, College of Medicine, 750 East Adams Street, Syracuse, NY 13210, USA.
Niland
Brian
B
Stancato
Christina
C
Verhoeven
Nanda M
NM
Van Der Knaap
Marjo S
MS
Jakobs
Cornelis
C
Brown
Lawrence M
LM
Vajda
Sandor
S
Banki
Katalin
K
Perl
Andras
A
D002478:Cells, Cultured; D002648:Child; D004789:Enzyme Activation / Q000235:genetics / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005347:Fibroblasts / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D006801:Humans; D008103:Liver Cirrhosis / Q000201:enzymology / Q000235:genetics; D008214:Lymphocytes / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000235:genetics* / Q000502:physiology; D011487:Protein Conformation; D012313:RNA / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics* / Q000502:physiology; D012694:Serine / Q000235:genetics* / Q000502:physiology; D014153:Transaldolase / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism
D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D012694:Serine; D012313:RNA; D014153:Transaldolase; D046988:Proteasome Endopeptidase Complex