Hole Hopping Across a Protein-Protein Interface.
Hole Hopping Across a Protein-Protein Interface.
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蛋白质-蛋白质界面上的空穴跳跃。
DOI：
10.1021/acs.jpcb.8b11982
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Takematsu K
中科院分区：
文献类型：
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作者：
Takematsu K
我们研究了铜绿单胞菌突变体tre126wwcui的光诱导空穴跳变，其中两个相邻的色氨酸残基（W124和W122）插入到CuIcenter和与H126咪唑配位的Re光敏剂(Re = ReI(H126)（CO)3(dmp)+, dmp = 4,7-二甲基-1,10-菲罗啉）之间。该突变体在水介质（≤40 μM）中光激发可在23 Å上产生70 ns的电子传递，产生长寿命（120 μs）的ReI(H126)(CO)3(dmp•-)wwcuii产物。在这些条件下，126fwcuimutant （F124, W122）没有氧化还原活性。当浓度增加到0.2-2 mM时，一个分子的Re光氧化剂的dmp配体与邻链上的W122 '吲哚紧密接触（3.8 Å）形成{Re126WWCuI}2和{Re126FWCuI}2。此外，{Re126WWCuI}2含有四个吲哚（3.3-3.7 Å）的界面色氨酸四联体。在这两个突变体中，二聚化打开了分子间的W122 '→//*Re ET通道（//表示蛋白质界面，*Re是光激发敏化剂）。激发态弛豫和ET在两个步骤（时间常数为~ 600 ps和~ 8 ns）中一起发生，导致含有Re(H126)(CO)3(dmp•-)//(W122•+)'单元的电荷分离态；然后（CuI） ‘在分子内（60 ~ 90 ns）被（W122•+）’氧化，形成ReI(H126)(CO)3(dmp•-)WWCuI//(CuII) '。与re126wwcui的23 Å、120 μs的步骤相比，在12 Å上发生的ReI(H126)(CO)3（dmp•-）→//(CuII) ' back ET为~ 1.6 μs。重要的是，二聚化使re126fwcui具有光反应性，并且与{Re126WWCuI}2的情况一样，将光产生的“孔”引导到最初未被光激发的分子上，从而缩短了ReI(H126)(CO)3(dmp•-)//CuII的寿命。虽然两个相邻的W124和W122吲哚显著增强了CuI→*赖分子多步ET，但{Re126WWCuI}2中的色氨酸四联体并不加速分子间电子传递；相反，它充当空穴存储和分子间和分子内ET通路之间的交叉单元。{Re126WWCuII}2或{Re126FWCuII}2的辐照也触发了分子间的W122 ‘→//*Re ET, Re(H126)(CO)3(dmp•-)//(W122•+)’电荷分离态通过~ 50 ns的ReI(H126)(CO)3(dmp•-)+→//(W122•+)'分子间电荷重组而衰变成基态。我们的发现揭示了控制蛋白质复合物中界面空穴/电子跳跃的因素，以及芳香氨基酸在加速远程电子传递中的作用。
We have investigated photoinduced hole hopping in aPseudomonas aeruginosaazurin mutantRe126WWCuI, where two adjacent tryptophan residues (W124 and W122) are inserted between the CuIcenter and a Re photosensitizer coordinated to a H126 imidazole (Re = ReI(H126)(CO)3(dmp)+, dmp = 4,7-dimethyl-1,10-phenanthroline). Optical excitation of this mutant in aqueous media (≤40 μM) triggers 70 ns electron transport over 23 Å, yielding a long-lived (120 μs) ReI(H126)(CO)3(dmp•–)WWCuIIproduct. TheRe126FWCuImutant (F124, W122) is not redox-active under these conditions. Upon increasing the concentration to 0.2–2 mM,{Re126WWCuI}2and{Re126FWCuI}2are formed with the dmp ligand of the Re photooxidant of one molecule in close contact (3.8 Å) with the W122′ indole on the neighboring chain. In addition,{Re126WWCuI}2contains an interfacial tryptophan quadruplex of four indoles (3.3–3.7 Å apart). In both mutants, dimerization opens anintermolecular W122′ → //*Re ET channel (// denotes the protein interface, *Re is the optically excited sensitizer). Excited-state relaxation and ET occur together in two steps (time constants of ∼600 ps and ∼8 ns) that lead to a charge-separated state containing a Re(H126)(CO)3(dmp•–)//(W122•+)′ unit; then (CuI)′ is oxidizedintramolecularly (60–90 ns) by (W122•+)′, forming ReI(H126)(CO)3(dmp•–)WWCuI//(CuII)′. The photocycle is closed by ∼1.6 μs ReI(H126)(CO)3(dmp•–) → //(CuII)′ back ET that occurs over 12 Å, in contrast to the 23 Å, 120 μs step inRe126WWCuI. Importantly, dimerization makesRe126FWCuIphotoreactive and, as in the case of{Re126WWCuI}2, channels the photoproduced “hole” to the molecule that was not initially photoexcited, thereby shortening the lifetime of ReI(H126)(CO)3(dmp•–)//CuII. Although two adjacent W124 and W122 indoles dramatically enhance CuI→ *Reintramolecular multistep ET, the tryptophan quadruplex in{Re126WWCuI}2does not accelerateintermolecular electron transport; instead, it acts as a hole storage and crossover unit betweeninter- andintramolecular ET pathways. Irradiation of{Re126WWCuII}2or{Re126FWCuII}2also triggersintermolecular W122′ → //*Re ET, and the Re(H126)(CO)3(dmp•–)//(W122•+)′ charge-separated state decays to the ground state by ∼50 ns ReI(H126)(CO)3(dmp•–)+→ //(W122•+)′intermolecular charge recombination. Our findings shed light on the factors that control interfacial hole/electron hopping in protein complexes and on the role of aromatic amino acids in accelerating long-range electron transport.