Deletion of Ser-171 causes inactivation, proteasome-mediated degradation and complete deficiency of human transaldolase.

Abstract

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.

• Authors: Craig E Grossman, Brian Niland, Christina Stancato, Nanda M Verhoeven, Marjo S Van Der Knaap, Cornelis Jakobs, Lawrence M Brown, Sandor Vajda, Katalin Banki, Andras Perl
• Journal: The Biochemical journal (Biochem J) Vol. 382 Issue Pt 2 Pg. 725-31 (Sep 01 2004) ISSN: 1470-8728 [Electronic] England
• PMID: 15115436 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Enzyme Inhibitors
• Recombinant Proteins
• Serine
• RNA
• Transaldolase
• Proteasome Endopeptidase Complex

Topics

• Cells, Cultured
• Child
• Enzyme Activation (genetics, physiology)
• Enzyme Inhibitors (pharmacology)
• Female
• Fibroblasts (chemistry, enzymology, metabolism)
• Gene Expression Regulation, Bacterial (genetics)
• Gene Expression Regulation, Enzymologic (drug effects, genetics)
• Humans
• Liver Cirrhosis (enzymology, genetics)
• Lymphocytes (chemistry, enzymology, metabolism)
• Models, Molecular
• Mutagenesis, Site-Directed (genetics)
• Proteasome Endopeptidase Complex (genetics, physiology)
• Protein Conformation
• RNA (metabolism)
• Recombinant Proteins (biosynthesis, genetics)
• Sequence Deletion (genetics, physiology)
• Serine (genetics, physiology)
• Transaldolase (biosynthesis, deficiency, genetics, metabolism)