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Selenocysteine-dependent Enzymes: Structure, Function and Selenium-derived Mechanism.

Feilong Li1, Jian Gao2, Ye-Wang Zhang3

  • 1School of Grain Science and Technology, Jiangsu University of Science and Technology, Zhenjiang 212100, the People's Republic of China.

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|March 31, 2026
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Summary

Selenocysteine (Sec) enzymes show higher catalytic activity than cysteine (Cys) enzymes due to selenium's unique chemical properties. This review compares Sec and Cys enzymes, revealing Sec's advantages in catalysis and oxidative resistance.

Keywords:
catalytic activitycatalytic directionalitycysteineoxidative resistanceselenocysteine-dependent enzyme

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Area of Science:

  • Biochemistry and enzymology
  • Bioinorganic chemistry
  • Protein science

Background:

  • Selenocysteine (Sec) is the 21st proteinogenic amino acid, acting as a sulfur analog to cysteine (Cys).
  • Sec is crucial in the catalytic sites of Sec-dependent enzymes, imparting unique properties due to selenium's distinct chemistry.
  • These Sec-dependent enzymes differ significantly from their Cys-dependent counterparts in function and characteristics.

Purpose of the Study:

  • To systematically analyze and compare Sec-dependent enzymes with their Cys-dependent analogs.
  • To investigate differences in biological function, active-site structure, catalytic properties, and mechanistic insights.
  • To elucidate the relationship between Sec's chemical properties and enzyme catalytic advantages.

Main Methods:

  • Comparative analysis of well-characterized Sec-dependent enzymes and their natural/engineered Cys analogs.
  • Examination of active-site structures, catalytic mechanisms, and kinetic properties.
  • Review of literature focusing on enzyme function, catalytic efficiency, and oxidative resistance.

Main Results:

  • Sec-dependent enzymes consistently demonstrate higher catalytic activities than Cys analogs, despite similar architectures and mechanisms.
  • The kinetic advantage stems from selenolate's superior nucleophilicity and leaving-group ability compared to thiolate.
  • Sec-dependent redox enzymes exhibit enhanced oxidative resistance; Sec's acidity aids reductive reactions in formate dehydrogenases and hydrogenases.

Conclusions:

  • The distinct chemical properties of selenium in Sec confer significant catalytic advantages over cysteine.
  • Understanding the Sec-catalyst relationship provides a basis for engineering improved enzyme performance.
  • Compensatory mechanisms in some Cys-dependent enzymes highlight the evolutionary drive for catalytic efficiency.