Department of Biology, Kocaeli University, Umuttepe, Kocaeli 41380, Turkey.
School of Chemistry and Bioscience, Faculty of Life Sciences, University of Bradford, Bradford West Yorkshire BD7 1DP, UK.
Biochim Biophys Acta Proteins Proteom. 2021 Aug;1869(8):140662. doi: 10.1016/j.bbapap.2021.140662. Epub 2021 Apr 19.
Scytalidium catalase is a homotetramer including heme d in each subunit. Its primary function is the dismutation of HO to water and oxygen, but it is also able to oxidase various small organic compounds including catechol and phenol. The crystal structure of Scytalidium catalase reveals the presence of three linked channels providing access to the exterior like other catalases reported so far. The function of these channels has been extensively studied, revealing the possible routes for substrate flow and product release. In this report, we have focussed on the semi-conserved residue Val228, located near to the vinyl groups of the heme at the opening of the lateral channel. Its replacement with Ala, Ser, Gly, Cys, Phe and Ile were tested. We observed a significant decrease in catalytic efficiency in all mutants with the exception of a remarkable increase in oxidase activity when Val228 was mutated to either Ala, Gly or Ser. The reduced catalytic efficiencies are characterized in terms of the restriction of hydrogen peroxide as electron acceptor in the active centre resulting from the opening of lateral channel inlet by introducing the smaller side chain residues. On the other hand, the increased oxidase activity is explained by allowing the suitable electron donor to approach more closely to the heme. The crystal structures of V228C and V228I were determined at 1.41 and 1.47 Å resolution, respectively. The lateral channels of the V228C and V228I presented a broadly identical chain of arranged waters to that observed for wild-type enzyme.
裂褶菌过氧化氢酶是一个四聚体，每个亚基包含一个血红素 d。它的主要功能是将 HO 歧化为水和氧气，但它也能够氧化包括儿茶酚和苯酚在内的各种小分子有机化合物。裂褶菌过氧化氢酶的晶体结构揭示了三个相连的通道的存在，这些通道像迄今为止报道的其他过氧化氢酶一样提供了通向外部的途径。这些通道的功能已经得到了广泛的研究，揭示了底物流动和产物释放的可能途径。在本报告中，我们集中研究了位于侧通道开口处血红素的乙烯基附近的半保守残基 Val228。用 Ala、Ser、Gly、Cys、Phe 和 Ile 取代 Val228 进行了测试。我们观察到所有突变体的催化效率都显著降低，但 Val228 突变为 Ala、Gly 或 Ser 时，氧化酶活性显著增加。在活性中心中，由于侧通道入口的打开，过氧化氢作为电子受体受到限制，从而导致催化效率降低，这可以用引入较小侧链残基来解释。另一方面，氧化酶活性的增加可以解释为允许合适的电子供体更接近血红素。V228C 和 V228I 的晶体结构分别在 1.41 和 1.47 Å分辨率下确定。V228C 和 V228I 的侧通道呈现出与野生型酶观察到的大致相同的排列水链。
