The cytoplasmic loops of AgrC contribute to the quorum-sensing activity of Staphylococcus aureus
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The cytoplasmic loops of AgrC contribute to the quorum-sensing activity of Staphylococcus aureus§ Qian Huang†, Yihui Xie†, Ziyu Yang, Danhong Cheng, Lei He, Hua Wang, Qian Liu*, and Min Li* Department of Laboratory Medicine, RenJi Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200127, P. R. China (Received May 22, 2020 / Revised Sep 22, 2020 / Accepted Sep 25, 2020)
In Staphylococcus aureus, the accessory gene regulator (agr) quorum-sensing system is thought to play an important role in biofilm formation. The histidine kinase AgrC is one of the agr system components and activated by the self-generated auto-inducing peptide (AIP), which is released continuously into the extracellular environment during bacterial growth. The extracellular loops (Extra-loops) of AgrC are crucial for AIP binding. Here, we reported that the cytoplasmic loops (Cyto-loops) of AgrC are also involved in Agr activity. We identified S. aureus ST398 clinical isolates containing a naturally occurring single amino acid substitution (lysine to isoleucine) at position 73 of an AgrC Cyto-loop that exhibited significantly stronger biofilm formation and decreased Agr activity compared to the wild-type strain. A constructed strain containing the K73I point mutation in AgrC Cyto-loop continued to show a growth dependent induction of the agr system, although the growth dependent induction was delayed by about 6 h compared to the wild-type. In addition, a series of strains containing deletion mutants of the AgrC Cyto- and Extra-loops were constructed and revealed that the removal of the two Cyto-loops and Extra-loops 2 and 3 totally abolished the Agr activity and the growth-dependence on the agr system induction. Remarkably, the Extra-loop 1 deletion did not affect the Agr activity. In conclusion, the AgrC Cyto-loops play a crucial role in the S. aureus quorum-sensing activity. Keywords: Staphylococcus aureus, Agr, biofilm, loop, sensing Introduction Staphylococcus aureus causes several diseases, including acute infections by producing a repertoire of virulence factors, and persistent infections through biofilm formation (Archer, † These authors contributed equally to this work. *For correspondence. (Q. Liu) E-mail: [email protected]; Tel.: +8618 121369390; (M. Li) E-mail: [email protected]; Tel.: +8613918363998 § Supplemental material for this article may be found at http://www.springerlink.com/content/120956. Copyright ⓒ 2021, The Microbiological Society of Korea
1998). Bacterial biofilm is a complex community that has intrinsic resistance to the host immune defense and antibiotic treatment (Otto, 2013). Several regulators have been identified to play a significant role in the formation of S. aureus biofilm (Boles and Horswill, 2008). The staphylococcal quorum-sensing system, named accessory gene regulator (agr), inhibits biofilm formation by up-regulating the extracellular cysteine proteases SspB and ScpA (Mootz et al., 2013). The agr locus consist of two operons driven by the P2 and P3 promot
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