可扩散信号因子 (DSF) 是由众多革兰氏阴性菌产生和检测的群体感应自诱导物 (AI) 家族。DSF 家族 AI 是脂肪酸,它们的酰基链长度、分支和取代不同,但有一个共同的顺式-2 双键是他们活动所必需的。在人类和植物病原体中,DSF 调节多种表型,包括毒力因子表达、抗生素耐药性和生物膜扩散。尽管它们与人类健康和农业有着广泛的相关性,但它们的细胞受体识别 DSF 的分子基础仍然是个谜。在这里,我们报告了致病因子 R (RpfR) 的 DSF 受体调节的第一个结构-功能研究。我们展示了与伯克霍尔德氏菌复合的 RpfR DSF 结合域的 X 射线晶体结构DSF (BDSF),据我们所知,这是第一个与其 AI 复合的 DSF 受体结构。为了开始了解在生物学上重要的复合物中观察到的 BDSF-RpfR 接触的机械作用,我们还确定了 RpfR DSF 结合域与 BDSF 的非活性饱和异构体十二烷酸复合物的 X 射线晶体结构(C12:0)。除了这些配体-受体复合物结构外,我们还报告了一个以前被忽视的 RpfR 结构域的发现,并表明它结合并负向调节致病因子 F (RpfF) 的 DSF 合酶调节。我们已将此 RpfR 区域命名为 RpfF 相互作用 (FI) 域,并且我们已确定其单独的 X 射线晶体结构以及与 RpfF 的复合物。这些 X 射线晶体结构,顺式-2 双键到 DSF 函数。最后,我们表明,在整个细胞生长过程中,RpfF 产生的 BDSF 由 RpfR N-末端 FI 结构域进行翻译后控制,影响细菌第二信使双-(3'-5')-环二聚体的细胞浓度鸟苷一磷酸 (c-di-GMP)。因此,除了描述 DSF 与其受体的结合和特异性的分子基础外,我们还描述了调节细菌群体感应信号和第二信使信号转导的受体-合酶相互作用。
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Structural basis of DSF recognition by its receptor RpfR and its regulatory interaction with the DSF synthase RpfF
The diffusible signal factors (DSFs) are a family of quorum-sensing autoinducers (AIs) produced and detected by numerous gram-negative bacteria. The DSF family AIs are fatty acids, differing in their acyl chain length, branching, and substitution but having in common a cis-2 double bond that is required for their activity. In both human and plant pathogens, DSFs regulate diverse phenotypes, including virulence factor expression, antibiotic resistance, and biofilm dispersal. Despite their widespread relevance to both human health and agriculture, the molecular basis of DSF recognition by their cellular receptors remained a mystery. Here, we report the first structure–function studies of the DSF receptor regulation of pathogenicity factor R (RpfR). We present the X-ray crystal structure of the RpfR DSF-binding domain in complex with the Burkholderia DSF (BDSF), which to our knowledge is the first structure of a DSF receptor in complex with its AI. To begin to understand the mechanistic role of the BDSF–RpfR contacts observed in the biologically important complex, we have also determined the X-ray crystal structure of the RpfR DSF-binding domain in complex with the inactive, saturated isomer of BDSF, dodecanoic acid (C12:0). In addition to these ligand–receptor complex structures, we report the discovery of a previously overlooked RpfR domain and show that it binds to and negatively regulates the DSF synthase regulation of pathogenicity factor F (RpfF). We have named this RpfR region the RpfF interaction (FI) domain, and we have determined its X-ray crystal structure alone and in complex with RpfF. These X-ray crystal structures, together with extensive complementary in vivo and in vitro functional studies, reveal the molecular basis of DSF recognition and the importance of the cis-2 double bond to DSF function. Finally, we show that throughout cellular growth, the production of BDSF by RpfF is post-translationally controlled by the RpfR N-terminal FI domain, affecting the cellular concentration of the bacterial second messenger bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP). Thus, in addition to describing the molecular basis for the binding and specificity of a DSF for its receptor, we describe a receptor–synthase interaction regulating bacterial quorum-sensing signaling and second messenger signal transduction.