Structure and inhibition of a quorum sensing target from Streptococcus pneumoniae
Structure and inhibition of a quorum sensing target from Streptococcus pneumoniae
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DOI：
10.1021/bi061184i
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发表时间：
2006-10-31
期刊：
影响因子：
2.9
通讯作者：
Schramm, Vern L.
中科院分区：
文献类型：
--
作者：
Singh, Vipender;Shi, Wuxian;Schramm, Vern L.
肺炎链球菌5'-甲硫腺苷/S-腺苷高半胱氨酸水解酶（MTAN）催化其底物水解去腺苷化形成腺嘌呤和5-甲硫核糖或S-核糖高半胱氨酸（SRH）。MTAN在哺乳动物中未发现，但与细菌群体感应有关。MTAN基因的破坏会影响细菌的生长和致病性，使其成为抗生素设计的目标。动力学同位素效应和计算研究已经为大肠杆菌MTAN建立了解离的S（N）1过渡态，并且类似于过渡态的过渡态类似物是酶的强有力的抑制剂[Singh，V.，李，J.L.，努涅斯，S.，豪厄尔，P.L.，和施拉姆，V.L.（2005）生物化学44，11647 - 11659]。从S. pneumoniae与E. pneumoniae同源性为40%。coli MTAN，而S.肺炎支原体MTAN表现出明显不同的动力学和抑制特性。5'-甲硫基-Immucillin-A（MT-ImmmA）是一种类似于早期SN1过渡态的过渡态类似物。它是一种弱的S.肺炎MTAN，K-i为1.0 AM。X射线结构分析表明，S.具有MT-ImmA的肺炎MTAN表示在柔性疏水袋中具有甲硫基的二聚体。用苯基（PhT-ImmA）、甲苯基（p-TolT-ImmA）或乙基（EtT-ImmA）取代甲基增加了亲和力，分别得到335、60和40nM的Ki值。DADMe-免疫球蛋白是完全解离过渡态的几何和静电模拟物，结合比免疫球蛋白更紧密。MT-DADMe-Immucillin-A抑制的Ki值为24nM，并且用对-Cl-苯基取代5 "-甲基（p-Cl-PhT-DADMe-ImmmA）得到0.36nM的K-i * 值。相对于免疫球蛋白，DADMe-免疫球蛋白的抑制潜力支持了S.肺炎MTAN。X射线晶体结构中活性位接触的比较。coli和革兰氏阳性菌S.肺炎支原体MTAN与MT-ImmA的结合将预测相等的结合，然而大多数类似物与E.大肠杆菌酶。由于S的k（cat）/K-m，催化位点效率是造成这种差异的主要原因。MTAN相对于E. pneumoniae降低了845倍。coli MTAN中表达。
Streptococcus pneumoniae 5'-methylthioadenosine/S-adenosylhomocysteine hydrolase ( MTAN) catalyzes the hydrolytic deadenylation of its substrates to form adenine and 5-methylthioribose or S-ribosylhomocysteine ( SRH). MTAN is not found in mammals but is involved in bacterial quorum sensing. MTAN gene disruption affects the growth and pathogenicity of bacteria, making it a target for antibiotic design. Kinetic isotope effects and computational studies have established a dissociative S(N)1 transition state for Escherichia coli MTAN, and transition state analogues resembling the transition state are powerful inhibitors of the enzyme [ Singh, V., Lee, J. L., Nunez, S., Howell, P. L., and Schramm, V. L. ( 2005) Biochemistry 44, 11647-11659]. The sequence of MTAN from S. pneumoniae is 40% identical to that of E. coli MTAN, but S. pneumoniae MTAN exhibits remarkably distinct kinetic and inhibitory properties. 5'-Methylthio-Immucillin-A ( MT-ImmA) is a transition state analogue resembling an early SN1 transition state. It is a weak inhibitor of S. pneumoniae MTAN with a K-i of 1.0 AM. The X-ray structure of S. pneumoniae MTAN with MT-ImmA indicates a dimer with the methylthio group in a flexible hydrophobic pocket. Replacing the methyl group with phenyl ( PhT-ImmA), tolyl ( p-TolT-ImmA), or ethyl ( EtT-ImmA) groups increases the affinity to give Ki values of 335, 60, and 40 nM, respectively. DADMe-Immucillins are geometric and electrostatic mimics of a fully dissociated transition state and bind more tightly than Immucillins. MT-DADMe-Immucillin-A inhibits with a Ki value of 24 nM, and replacing the 5'-methyl group with p-Cl-phenyl ( p-Cl-PhT-DADMe-ImmA) gave a K-i* value of 0.36 nM. The inhibitory potential of DADMe-Immucillins relative to the Immucillins supports a fully dissociated transition state structure for S. pneumoniae MTAN. Comparison of active site contacts in the X-ray crystal structures of E. coli and S. pneumoniae MTAN with MT-ImmA would predict equal binding, yet most analogues bind 10(3)-10(4)-fold more tightly to the E. coli enzyme. Catalytic site efficiency is primarily responsible for this difference since k(cat)/K-m for S. pneumoniae MTAN is decreased 845-fold relative to that of E. coli MTAN.