Probing mammalian spermine oxidase enzyme-substrate complex through molecular modeling, site-directed mutagenesis and biochemical characterization

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.