单功能过氧化氢酶的高级结构

Crystal Structures of Monofunctional Catalases

单功能过氧化氢酶是在生物界广泛分布的抗氧化酶.近年来,人们在对单功能过氧化氢酶一级结构与生化性质深入研究的基础上,针对十几种单功能过氧化氢酶的高度保守的空间结构开展了研究.认识了其活性中心的血红素及周围保守残基,发现了酶的许多特殊结构,如方向不同的血红素,增强酶抗氧化性的侧链残基的共价键和保证酶高效催化的分子内通道等.本文综述了单功能过氧化氢酶空间结构研究现状,概括了酶构象的基本特点,分析了关注和争议较多的酶血红素、肽链侧链共价键及酶分子内通道等重点问题.深入研究单功能过氧化氢酶空间结构是一挑战性的课题,它将推动酶蛋白高级结构形成和酶催化模式等基础理论研究.

Monofunctional catalases （MC） are widely spread as antioxidant enzymes among all organisms to survive in oxic environments. More than ten highly conserved conformations of MC belonging to three phylogenetic clades have been identified based on X-ray crystallography studies involved in the primary structures and biochemical properties of MC. The subunits, functional domains, active heme-binding sites with the conserved neighboring amino acid residues, and the catalytic mechanism following the tetramerization of MC are subsequently elucidated. The crystal structures have revealed several distinct features of MC, such as the large MC subunits have peculiar covalent bonds between the side chains of the amino acids adjacent to the heme, which contribute to the antioxidant activities. The Clade Ⅲ MCs have the His of active sites situated above the ring Ⅲof the heine （His-Ⅲ orientation）, whereas the Clade Ⅰ and Ⅱ MCs have His-Ⅳ orientation with the His located above the ring Ⅳ of the heme. All of MCs have inner channel structures to allow the access of the deeply buried heme at the active sites, ensuring the efficient catalytic conformation via the ＂flow through mechanism＂. Perspective studies are required to investigate the MC quaternary structures, which will bring further insights of the MC main chain intricate conformation with heme in relation to the MC biological characteristics. The results will provide clues to develop strategies for the modification and application of the enzyme.