Characterization of the molecular basis of the Drosophila mutations in carboxypeptidase D: Effect on enzyme activity and expression

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Abstract

Carboxypeptidase D (CPD) functions in the processing of proteins and peptides in the secretory pathway. Drosophila CPD is encoded by the silver gene (svr), which is differentially spliced to produce long transmembrane protein forms with three metallocarboxypeptidase (CP)-like domains and short soluble forms with a single CP domain. Many svr mutants have been reported, but the precise molecular defects have not been previously determined. In the present study, three mutant lines were characterized. svrPG33 mutants do not survive past the early larval stage. These mutants have a P-element insertion within exon 1B upstream of the initiation ATG, which greatly reduces mRNA levels of all forms of CPD. Both svr1 and svrpoi mutants are viable, with a silvery body color and pointed wings. The wing shape is generally similar between these two mutants, although svrpoi mutants have smaller wings. The svr1 gene has a three-nucleotide deletion in exon 6, removing a leucine in a region of the protein predicted to function as a folding domain for the second CP-like domain. svrpoi has a 1072-bp duplication of the gene that introduces a stop codon into the open reading frame, causing the truncation of the protein in the middle of the second CP-like domain. Both deletions eliminate enzyme activity of the second CP-like domain and appear to cause the misfolding of the protein. This greatly reduces the levels of the long forms of CPD protein but do not affect the levels of the short forms. Taken together, these findings suggest that lethal and viable svr alleles differ in which protein forms are affected. Flies that retain the short form are viable, whereas flies that are missing all forms of CPD do not survive past the early larval stages.

Original languageEnglish (US)
Pages (from-to)13844-13852
Number of pages9
JournalJournal of Biological Chemistry
Volume281
Issue number19
DOIs
StatePublished - May 12 2006

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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