放线菌代谢产物结构不同、功能各异,如:吡咯并苯二氮卓类抗肿瘤化合物(pyrrolobenzodiazepines, PBDs),林可酰胺类抗生素,群体感应分子hormaomycin和抗菌素griselimycin(Fig. 1A)。这些化合物的共同特征是在其结构中掺入了酪氨酸或I-亮氨酸衍生的4-烷基-I-脯氨酸衍生物(l-tyrosine- or l-leucine-derived 4-alkyl-l-proline derivatives, APDs)骨架。PBD代表了一类序列选择性DNA烷基化剂,能够与DNA小沟结合从而行使卓越的抗肿瘤活性,目前已有几种基于PBD的抗癌药物正在进行临床前/临床试验中评估。林可酰胺则通过结合50S核糖体亚基的肽转移酶位点来抑制细菌蛋白质合成。有文献报道:在PBD和林可酰胺类药物中,APD侧链对生物活性具有积极作用。
Figure 1. (A) Metabolites with an APD moiety (in red), for which BGCs (B) are published and Apd6 proteins were characterized. The apd gene sub-clusters are colored (apd1-apd5 in blue,apd6 in red).
Scheme 1. (A) Proposed scheme of the L-tyrosine-derived APD biosynthetic pathway. (B) Scheme of the L-leucinederived APD biosynthetic pathway, which involves Apd6 GriH from griselimycin biosynthesis.
Figure 2. In vitro reactions with the 5a substrate converted by Apd6 proteins: (A) LmbY from lincomycin biosynthesis, (B) Por15 from PBD biosynthesis, (C) HrmD from hormaomycin biosynthesis, and (D) GriH from griselimycin biosynthesis.
Figure 3. Crystal structures of (A) PBD anthramycin covalently bound to DNA strands and (B) lincomycin targeting the peptidyl transferase center in the 50S ribosomal subunit ofStaphylococcus aureus.
Scheme 2. Proposed distinct catalytic mechanisms of Apd6 from (A) PBD, hormaomycin, griselimycin; and (B) from lincomycin and griselimycin biosyntheses. All tested Apd6 accept5a as a substrate. 本文通过系统发育分析表明:Apd6是来自LLHT超家族的第一个特征化链霉菌F420/ F420H2依赖性酶同时也是第一个LLHT F420/F420H2依赖性蛋白。研究人员还通过生信分析鉴定了数十种推测的Apd6蛋白,这些蛋白可能与新型APD化合物的生物合成有关,并且可能与各种L-脯氨酸样前体的生物合成和代谢过程有关。 本文报告了APDs生物合成途径的最终步骤,详细解析了由F420H2依赖的Apd6还原酶催化相同底物而形成不同APD的原因。Apd6的催化差异性决定了lincomycin的完全饱和APD骨架以及PBDs的不饱和APD骨架的形成机制,这为二者结合其独特的生物学靶标提供了最佳的分子形态。