4HTR

N149W variant of SiRHP bound to sulfite

4HTR の概要

• エントリーDOI: 10.2210/pdb4htr/pdb
• 関連するPDBエントリー: 4G38 4G39
• 分子名称: Sulfite reductase [NADPH] hemoprotein beta-component, SULFITE ION, SODIUM ION, ... (6 entities in total)
• 機能のキーワード: oxidoreductase, siroheme-binding protein, iron-sulfur cluster, s/nirr, oxidoreductase-substrate complex, oxidoreductase/substrate
• 由来する生物種: Escherichia coli
• タンパク質・核酸の鎖数: 1
• 化学式量合計: 58391.50

構造登録者

Smith, K.W.,Stroupe, M.E. (登録日: 2012-11-01, 公開日: 2013-01-16, 最終更新日: 2023-12-27)

主引用文献

Smith, K.W.,Stroupe, M.E.
Mutational analysis of sulfite reductase hemoprotein reveals the mechanism for coordinated electron and proton transfer.
Biochemistry, 51:9857-9868, 2012

PubMed Abstract: Sulfite reductase catalyzes the six-electron reduction of sulfite to sulfide. The active site, found in the hemoprotein subunit (SiRHP), sits on the distal face of a negatively charged porphyrinoid called siroheme whose central iron atom is coupled to a proximal Fe(4)S(4) cluster. Four positively charged amino acids are positioned around the active site cavity. Together, these two arginines (R83 and R153) and two lysines (K215 and K217) mitigate the negative charge on the siroheme macrocycle. They also serve as a cage around the distally bound anion that tightens when substrate binds and an active site loop clamps down. Structures of native SiRHP point to these amino acids as being important, but their specific roles are ill-defined. Here, we have altered those four active site amino acids and one amino acid on the flexible loop (N149) to probe their roles in SiRHP activity. None of these positively charged residues is required for electron transfer, but only R83S and N149W variants can produce a fully reduced product. By measuring the electrons used per unit of reduced sulfur released, we show that K215, R153, and K217 are responsible for intermediate and late proton transfers, whereas N149 and R153 play a role in the structure of the flexible loop that controls anion binding and release. R83 is primarily responsible for siroheme binding. Together, the activities and structures of these variants reveal specific roles for each in anion binding and in coupled proton transfer that facilitates electron transfer.

PubMed: 23153334
DOI: 10.1021/bi300947a

実験手法

X-RAY DIFFRACTION (1.6 Å)