Department of Biology, University Roma Tre, Viale Guglielmo Marconi 446, 00146, Rome, Italy.
Amino Acids. 2011 Apr;40(4):1115-26. doi: 10.1007/s00726-010-0735-8. Epub 2010 Sep 14.
Spermine oxidase (SMO) and acetylpolyamine oxidase (APAO) are FAD-dependent enzymes that are involved in the highly regulated pathways of polyamine biosynthesis and degradation. Polyamine content is strictly related to cell growth, and dysfunctions in polyamine metabolism have been linked with cancer. Specific inhibitors of SMO and APAO would allow analyzing the precise role of these enzymes in polyamine metabolism and related pathologies. However, none of the available polyamine oxidase inhibitors displays the desired characteristics of selective affinity and specificity. In addition, repeated efforts to obtain structural details at the atomic level on these two enzymes have all failed. In the present study, in an effort to better understand structure-function relationships, SMO enzyme-substrate complex has been probed through a combination of molecular modeling, site-directed mutagenesis and biochemical studies. Results obtained indicate that SMO binds spermine in a similar conformation as that observed in the yeast polyamine oxidase FMS1-spermine complex and demonstrate a major role for residues His82 and Lys367 in substrate binding and catalysis. In addition, the SMO enzyme-substrate complex highlights the presence of an active site pocket with highly polar characteristics, which may explain the different substrate specificity of SMO with respect to APAO and provide the basis for the design of specific inhibitors for SMO and APAO.
精胺氧化酶（SMO）和乙酰多胺氧化酶（APAO）是依赖黄素腺嘌呤二核苷酸（FAD）的酶，它们参与多胺生物合成和降解的高度调控途径。多胺含量与细胞生长密切相关，多胺代谢功能障碍与癌症有关。SMO 和 APAO 的特异性抑制剂将允许分析这些酶在多胺代谢和相关病理中的精确作用。然而，现有的多胺氧化酶抑制剂都没有表现出所需的选择性亲和力和特异性特征。此外，为了在原子水平上获得这两种酶的结构细节，人们进行了多次尝试，但都失败了。在本研究中，为了更好地了解结构-功能关系，通过分子建模、定点突变和生化研究的组合，对 SMO 酶-底物复合物进行了探测。结果表明，SMO 以与酵母多胺氧化酶 FMS1-精胺复合物中观察到的相似构象结合精胺，并证明残基 His82 和 Lys367 在底物结合和催化中起主要作用。此外，SMO 酶-底物复合物突出了具有高度极性特征的活性口袋的存在，这可能解释了 SMO 相对于 APAO 的不同底物特异性，并为 SMO 和 APAO 的特异性抑制剂的设计提供了基础。
