Abstract：
The docking of an acyl carrier protein (ACP) domain with a downstream ketosynthase (KS) domain in each module of a polyketide synthase (PKS) helps ensure accurate biosynthesis. If the polyketide chain bound to the ACP has been properly modified by upstream processing enzymes and is compatible with gatekeeping residues in the KS tunnel, a transacylation reaction can transfer it from the 18.1-Å phosphopantetheinyl arm of the ACP to the reactive cysteine of the KS. AlphaFold-Multimer predicts a general interface for these transacylation checkpoints. Half of the solutions obtained for 50 ACP/KS pairs show the KS motif TxLGDP forming the first turn of an α-helix, as in reported structures, while half show it forming a type I β-turn not previously observed. Solutions with the latter conformation may represent how these domains are relatively positioned during the transacylation reaction, as the entrance to the KS active site is relatively open and the phosphopantetheinylated ACP serine and the reactive KS cysteine are relatively closer-17.2 versus 20.9 Å, on average. To probe the predicted interface, 20 mutations were made to KS surface residues within the model triketide lactone synthase P1-P6-P7. The activities of these mutants are consistent with the proposed interface.
摘要：
酰基载体蛋白(ACP)结构域与聚酮合酶(PKS)的每个模块中的下游酮合酶(KS)结构域的对接有助于确保准确的生物合成。如果与ACP结合的聚酮化合物链已被上游加工酶适当修饰，并且与KS隧道中的守门残基相容，转酰化反应可以将其从ACP的18.1-µ磷酸氨基臂转移到KS的反应性半胱氨酸。AlphaFold-Multimer预测这些转酰化检查点的通用接口。为50个ACP/KS对获得的解决方案中，有一半显示了KS基序TxLGDP形成了α螺旋的第一圈，在报告的结构中，而一半显示它形成了以前没有观察到的I型β转角。具有后一种构象的溶液可以代表这些结构域在转酰化反应期间是如何相对定位的。由于KS活性位点的入口相对开放，并且磷酸化的ACP丝氨酸和反应性KS半胱氨酸相对更接近-17.2比20.9，平均而言。要探测预测的界面，对模型三酮内酯合酶P1-P6-P7内的KS表面残基进行20个突变。这些突变体的活动与所提出的界面一致。
