Biochemical characterisation of methanethiol oxidase: a key enzyme of volatile organosulfur compound degradation

我们建议研究一种细菌酶的性质，这种酶能转化一种恶臭、有毒的气态有机硫化合物。甲烷乙硫醇氧化酶转化甲烷乙硫醇--一种有腐烂卷心菜气味的气体--这是自然界中一种重要的硫化合物。甲硫醇催化反应的产物是甲醛、硫化氢（臭鸡蛋的气味）和过氧化氢（一种在接触式透镜消毒液中用作漂白剂的化学物质）。甲烷乙醇氧化酶的分子和催化性质知之甚少。我们提出的工作将提供对甲硫醇降解生物化学的基本见解，这一过程在全球范围内仅在海洋中就造成约3亿至5亿吨硫的周转，其中甲硫醇作为气候冷却气体（二甲基硫醚）及其前体分子（二甲基磺基丙酸酯）的降解产物而发生。甲硫醇在食品和饮料中起着风味化合物的作用，但当它浓度过高时，也会导致我们认为的异味。在工业背景下，甲硫醇作为本体溶剂（二甲亚砜）的降解产物也是重要的，并且可以想象，甲硫醇氧化酶可以作为工业生物催化剂找到应用。我们的初步数据还表明，这种酶可能与细胞内蛋白质复合物中的其他酶协同工作，这可能在某种程度上保护它免受有毒中间体的影响，并可能增强其功能。这种酶复合物也将进一步研究。我们刚刚发现的甲硫氨酸氧化酶的一个有趣的方面是，这种细菌酶是由一个基因编码的，以前没有任何信息表明它的功能。因此，进一步研究该酶是有意义的，特别是因为存在由包括人类在内的动物的基因组编码的类似酶，其功能同样知之甚少。因此，更详细地研究这种细菌酶，可能会揭示一种蛋白质的进化，这种蛋白质也存在于我们的体内。表征酶的最终目的是阐明其三维结构。虽然这不是该项目的计划，但我们的目标是通过生产可以通过X射线衍射分析表征的酶晶体来实现这一目标。这将需要使用重组DNA技术，这将允许产生足够量的用于结晶的酶。

We propose to characterise the properties of a bacterial enzyme that converts a foul smelling, toxic gaseous organic sulfur compound. Methanethiol oxidase converts methanethiol - a gas smelling of rotten cabbage - which is an important sulfur compound in nature. The products of the methanethiol catalysed reaction are formaldehyde, hydrogen sulfide (smells of rotten eggs) and hydrogen peroxide (a chemical that is used as a bleaching agent in contact lens disinfection fluids). Very little is known of the molecular and catalytic properties of methanethiol oxidases. The work we propose will provide fundamental insights into the biochemistry of methanethiol degradation, a process that on a global scale is responsible for turnover of some 300-500 million tons of sulfur in the oceans alone, where methanethiol occurs as a degradation product of a climate cooling gas (dimethylsulfide) and its precursor molecule (dimethylsulfoniopropionate). Methanethiol plays a role as a flavour compound in foods and beverages, but can also contribute to what we perceive as off-flavours when it occurs at too high concentrations. In an industrial context, methanethiol is also significant as a degradation product of bulk solvents (dimethylsulfoxide) and it is conceivable that methanethiol oxidase could find application as an industrial biocatalyst. Our preliminary data also indicate that this enzyme may work in concert with other enzymes in a complex of proteins inside the cell, which may protect it to some degree from its toxic intermediates and may enhance its function. This enzyme complex will also be studied further. An interesting aspect of methanethiol oxidase that we have just discovered is that this bacterial enzyme is encoded by a gene for which there has not been any information indicating its function previously. It is hence of interest to further investigate the enzyme, in particular as there are similar enzymes encoded by genomes of animals including humans on whose function similarly little is known. Thus, studying this bacterial enzyme in more detail, may shed light on the evolution of a type of protein which is also found in our bodies. The ultimate goal of characterising an enzyme is to elucidate its three dimensional structure. While this is not planned in this project, we aim to make the first step towards achieving that goal by producing crystals of the enzyme that can be characterised by X-ray diffraction analysis. This will require using recombinant DNA technology, which will allow to produce sufficient amounts of the enzyme for crystallisation.