Identification and conformer analysis of a novel redox-active motif, Pro-Ala-Ser-Cys-Cys-Ser, in Drosophila thioredoxin reductase by semiempirical molecular orbital calculation

Mitsuhiko Kuwahara, Takashi Tamura, Kentaro Kawamura, Kenji Inagaki

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Mammalian thioredoxin reductases (Trx Rs) contain selenium as selenocysteine (Sec) in the C-terminal redox center-Gly-Cys-Sec-Gly-OH to reduce Trx and other substrates; a Sec-to-Cys substitution in mammalian TrxR yields an almost inactive enzyme. The corresponding tetrapeptide sequence in Drosophila melanogaster TrxR (Dm-TrxR),-Ser-Cys-Cys-Ser-OH, endows the orthologous enzyme with a catalytic competence similar to mammalian selenoenzymes, but implementation of the Ser-containing tetrapeptide sequence SCCS into the mammalian enzyme does not restore the activity of the Sec-to-Cys mutant form (turnover number <2/min). MOPAC calculation suggested that the C-terminal hexapeptide Pro-Ala-Ser-Cys-Cys-Ser-OH functions as a redox center that alleviates the necessity for selenium in Dm-TrxR, and a mutant form of human lung TrxR that mimics this hexapeptide sequence showed improved catalytic turnover (17.4/min for DTNB and 13.2/min for E. coli trx) compared to the Sec-to-Cys mutant. MOPAC calculation also suggested that the dominant form of the Procontaining hexapeptide is a C+ conformation, which perhaps has a catalytic advantage in facile reduction of the intramolecular disulfide bond between Cys497 and Cys498 by the N-terminal redox center in the neighboring subunit.

Original languageEnglish
Pages (from-to)516-521
Number of pages6
JournalBioscience, Biotechnology and Biochemistry
Volume75
Issue number3
DOIs
Publication statusPublished - Apr 13 2011

Keywords

  • Drosophila melanogaster
  • Redox motif
  • Selenocysteine
  • Semiempirical molecular orbital calculation
  • Thioredoxin reductase

ASJC Scopus subject areas

  • Biotechnology
  • Analytical Chemistry
  • Biochemistry
  • Applied Microbiology and Biotechnology
  • Molecular Biology
  • Organic Chemistry

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