Structural features of PhoX, one of the phosphate-binding proteins from Pho regulon of <i>Xanthomonas citri</i>

In Escherichia coli, the ATP-Binding Cassette transporter for phosphate is encoded by the pstSCAB operon. PstS is the periplasmic component responsible for affinity and specificity of the system and has also been related to a regulatory role and chemotaxis during depletion of phosphate. Xanthomonas citri has two phosphate-binding proteins: PstS and PhoX, which are differentially expressed under phosphate limitation. In this work, we focused on PhoX characterization and comparison with PstS. The PhoX three-dimensional structure was solved in a closed conformation with a phosphate engulfed in the binding site pocket between two domains. Comparison between PhoX and PstS revealed that they originated from gene duplication, but despite their similarities they show significant differences in the region that interacts with the permeases.在大肠杆菌（Escherichia coli）中，负责磷酸盐转运的ATP结合盒转运蛋白（ATP-Binding Cassette transporter）由pstSCAB操纵子（pstSCAB operon）编码。PstS作为该系统的周质组分，负责维持其转运亲和力与特异性，同时也被证实与磷酸盐耗尽过程中的调控作用及趋化性相关。柑橘黄单胞菌（Xanthomonas citri）存在两种磷酸盐结合蛋白：PstS与PhoX，二者在磷酸盐限制条件下呈现差异表达特征。本研究聚焦于PhoX的表征分析，并将其与PstS进行对比。研究中解析了PhoX的闭合构象三维结构，其两个结构域之间的结合位点口袋内包裹有一个磷酸盐分子。通过比对PhoX与PstS发现，二者起源于基因复制事件；尽管二者具有较高的结构与序列相似性，但在与通透酶相互作用的区域存在显著差异。