PMID: 12435857

 

    Legend: Gene, Sites

Title : Lack of plasma membrane targeting of a G172D mutant thiamine transporter derived from Rogers syndrome family

Abstract :
  1. BACKGROUND: Rogers syndrome, also known as thiamine responsive megaloblastic anemia ( TRMA ), is an autosomal recessive disorder resulting in megaloblastic anemia, diabetes mellitus and sensorineural deafness
  2. The gene associated with Rogers syndrome encodes for a plasma membrane thiamine transporter, THTR-1 , a member of the solute carrier family that includes its homologue THTR-2 and the reduced folate carrier
  3. MATERIALS AND METHODS: Using transient expression of wild-type and a missense mutant THTR-1 protein , derived from a TRMA family, in different cell lines and immunodetection analysis, we determined the expression, posttranslational modification, and subcellular localization of the wild-type and G172D mutant THTR-1
  4. The transport activity of the transfected THTR-1 proteins was measured using a [(3) H ] thiamine uptake assay
  5. RESULTS: The mutant THTR-1 protein was undetectable in transfected cells grown at 37 degrees C but was readily expressed in transfected cells cultured at 28 degrees C, thereby allowing for further biochemical and functional analysis
  6. In contrast to its fully glycosylated wild-type mature protein , the mutant THTR-1 protein underwent only the initial stage of N-linked glycosylation
  7. The failure to undergo a complete glycosylation resulted in the lack of plasma membrane targeting and confinement of the mutant THTR-1 to the Golgi and endoplasmic reticulum (ER) compartment
  8. Consistently, either treatment with tunicamycin or substitution of the THTR-1 consensus N-glycosylation acceptor asparagine 63 with glutamine , abolished its glycosylation and plasma membrane targeting
  9. CONCLUSIONS: Taken collectively, these results suggest that the G172D mutation presumably misfolded THTR-1 protein that fails to undergo a complete glycosylation, is retained in the Golgi-ER compartment and thereby cannot be targeted to the plasma membrane
  10. Finally, transfection studies revealed that the mutant G172D THTR-1 failed to transport thiamine
  11. This is the first molecular and functional characterization of a missense mutant THTR-1 derived from a family with Rogers syndrome
Output (sent_index, trigger, protein, sugar, site):
  • 6. glycosylated, , protein, -, -
  • 9. glycosylation, , THTR-1 protein, -, -
Output(Part-Of) (sent_index, protein, site):
  • 8. THTR-1, asparagine 63
*Output_Site_Fusion* (sent_index, protein, sugar, site):

 

 

Protein NCBI ID SENTENCE INDEX
THTR-1 protein 10560 3,5,6,9
THTR-2 80704 2
G172D THTR-1 10560 10
THTR-1 10560 2,3,7,8,11
THTR-1 proteins 10560 4