Chen Zhi-wei, Hassan-Abdulah Alshaimaa, Zhao Gouhua, Jorns Marilyn Schuman, Mathews F Scott
Washington University School of Medicine, St. Louis, MO 63110, USA.
J Mol Biol. 2006 Jul 28;360(5):1000-18. doi: 10.1016/j.jmb.2006.05.067. Epub 2006 Jun 15.
The crystal structure of heterotetrameric sarcosine oxidase (TSOX) from Pseudomonas maltophilia has been determined at 1.85 A resolution. TSOX contains three coenzymes (FAD, FMN and NAD+), four different subunits (alpha, 103 kDa; beta, 44 kDa; gamma, 21 kDa; delta, 11 kDa) and catalyzes the oxidation of sarcosine (N-methylglycine) to yield hydrogen peroxide, glycine and formaldehyde. In the presence of tetrahydrofolate, the oxidation of sarcosine is coupled to the formation of 5,10-methylenetetrahydrofolate. The NAD+ and putative folate binding sites are located in the alpha-subunit. The FAD binding site is in the beta-subunit. FMN is bound at the interface of the alpha and beta-subunits. The FAD and FMN rings are separated by a short segment of the beta-subunit with the closest atoms located 7.4 A apart. Sulfite, an inhibitor of oxygen reduction, is bound at the FMN site. 2-Furoate, a competitive inhibitor with respect to sarcosine, is bound at the FAD site. The sarcosine dehydrogenase and 5,10-methylenetetrahydrofolate synthase sites are 35 A apart but connected by a large internal cavity (approximately 10,000 A3). An unexpected zinc ion, coordinated by three cysteine and one histidine side-chains, is bound to the delta-subunit. The N-terminal half of the alpha subunit of TSOX (alphaA) is closely similar to the FAD-binding domain of glutathione reductase but with NAD+ replacing FAD. The C-terminal half of the alpha subunit of TSOX (alphaB) is similar to the C-terminal half of dimethylglycine oxidase and the T-protein of the glycine cleavage system, proteins that bind tetrahydrofolate. The beta-subunit of TSOX is very similar to monomeric sarcosine oxidase. The gamma-subunit is similar to the C-terminal sub-domain of alpha-TSOX. The delta-subunit shows little similarity with any PDB entry. The alphaA domain/beta-subunit sub-structure of TSOX closely resembles the alphabeta dimer of L-proline dehydrogenase, a heteroctameric protein (alphabeta)4 that shows highest overall similarity to TSOX.
嗜麦芽窄食单胞菌异源四聚体肌氨酸氧化酶（TSOX）的晶体结构已在1.85 Å分辨率下确定。TSOX含有三种辅酶（FAD、FMN和NAD⁺）、四个不同的亚基（α，103 kDa；β，44 kDa；γ，21 kDa；δ，11 kDa），并催化肌氨酸（N-甲基甘氨酸）氧化生成过氧化氢、甘氨酸和甲醛。在四氢叶酸存在下，肌氨酸的氧化与5,10-亚甲基四氢叶酸的形成偶联。NAD⁺和假定的叶酸结合位点位于α亚基中。FAD结合位点在β亚基中。FMN结合在α和β亚基的界面处。FAD和FMN环被β亚基的一小段隔开，最近的原子相距7.4 Å。亚硫酸盐是氧还原的抑制剂，结合在FMN位点。2-糠酸盐是肌氨酸的竞争性抑制剂，结合在FAD位点。肌氨酸脱氢酶和5,10-亚甲基四氢叶酸合酶位点相距35 Å，但通过一个大的内部腔（约10,000 ų）相连。一个意想不到的锌离子由三个半胱氨酸和一个组氨酸侧链配位，结合在δ亚基上。TSOX的α亚基的N端一半（αA）与谷胱甘肽还原酶的FAD结合结构域非常相似，但NAD⁺取代了FAD。TSOX的α亚基的C端一半（αB）与二甲基甘氨酸氧化酶的C端一半以及甘氨酸裂解系统的T蛋白相似，这些蛋白结合四氢叶酸。TSOX的β亚基与单体肌氨酸氧化酶非常相似。γ亚基与α-TSOX的C端亚结构域相似。δ亚基与任何PDB条目几乎没有相似性。TSOX的αA结构域/β亚基亚结构与L-脯氨酸脱氢酶的αβ二聚体非常相似，L-脯氨酸脱氢酶是一种异八聚体蛋白（αβ）₄，与TSOX显示出最高的总体相似性。
