Eustáquio Alessandra S, Pojer Florence, Noel Joseph P, Moore Bradley S
Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
Nat Chem Biol. 2008 Jan;4(1):69-74. doi: 10.1038/nchembio.2007.56. Epub 2007 Dec 2.
Halogen atom incorporation into a scaffold of bioactive compounds often amplifies biological activity, as is the case for the anticancer agent salinosporamide A (1), a chlorinated natural product from the marine bacterium Salinispora tropica. Significant effort in understanding enzymatic chlorination shows that oxidative routes predominate to form reactive electrophilic or radical chlorine species. Here we report the genetic, biochemical and structural characterization of the chlorinase SalL, which halogenates S-adenosyl-L-methionine (2) with chloride to generate 5'-chloro-5'-deoxyadenosine (3) and L-methionine (4) in a rarely observed nucleophilic substitution strategy analogous to that of Streptomyces cattleya fluorinase. Further metabolic tailoring produces a halogenated polyketide synthase substrate specific for salinosporamide A biosynthesis. SalL also accepts bromide and iodide as substrates, but not fluoride. High-resolution crystal structures of SalL and active site mutants complexed with substrates and products support the S(N)2 nucleophilic substitution mechanism and further illuminate halide specificity in this newly discovered halogenase family.
将卤原子引入生物活性化合物的骨架中通常会增强其生物活性，抗癌药物沙利霉素A（1）就是这样一个例子，它是一种来自热带盐孢菌的含氯天然产物。在理解酶促氯化反应方面的大量努力表明，氧化途径在形成活性亲电或自由基氯物种中占主导地位。在此，我们报告了氯化酶SalL的遗传学、生物化学和结构特征，它通过与氯离子对S-腺苷-L-甲硫氨酸（2）进行卤化反应，以一种类似于卡特链霉菌氟化酶的罕见亲核取代策略生成5'-氯-5'-脱氧腺苷（3）和L-甲硫氨酸（4）。进一步的代谢修饰产生了一种卤化聚酮合酶底物，该底物对沙利霉素A的生物合成具有特异性。SalL也接受溴化物和碘化物作为底物，但不接受氟化物。SalL与底物和产物复合的高分辨率晶体结构支持了SN2亲核取代机制，并进一步阐明了这个新发现的卤化酶家族中的卤化物特异性。
