title: The extracytoplasmic linker peptide of the sensor protein SaeS tunes the kinase activity required for staphylococcal virulence in response to host signals.
abstract: Bacterial pathogens often employ two-component systems (TCSs), typically consisting of a sensor kinase and a response regulator, to control expression of a set of virulence genes in response to changing host environments. In Staphylococcus aureus, the SaeRS TCS is essential for in vivo survival of the bacterium. The intramembrane-sensing histidine kinase SaeS contains, along with a C-terminal kinase domain, a simple N-terminal domain composed of two transmembrane helices and a nine amino acid-long extracytoplasmic linker peptide. As a molecular switch, SaeS maintains low but significant basal kinase activity and increases its kinase activity in response to inducing signals such as human neutrophil peptide 1 (HNP1). Here we show that the linker peptide of SaeS controls SaeS's basal kinase activity and that the amino acid sequence of the linker peptide is highly optimized for its function. Without the linker peptide, SaeS displays aberrantly elevated kinase activity even in the absence of the inducing signal, and does not respond to HNP1. Moreover, SaeS variants with alanine substitution of the linker peptide amino acids exhibit altered basal kinase activity and/or irresponsiveness to HNP1. Biochemical assays reveal that those SaeS variants have altered autokinase and phosphotransferase activities. Finally, animal experiments demonstrate that the linker peptide-mediated fine tuning of SaeS kinase activity is critical for survival of the pathogen. Our results indicate that the function of the linker peptide in SaeS is a highly evolved feature with very optimized amino acid sequences, and we propose that, in other SaeS-like intramembrane sensing histidine kinases, the extracytoplasmic linker peptides actively fine-control their kinases.
authors: Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest,Gary, Indiana, United States of America.
authors: Qian
authors: Q
authors: Liu
authors: Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest,Gary, Indiana, United States of America.
authors: Hoonsik
authors: H
authors: Cho
authors: Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest,Gary, Indiana, United States of America.
authors: Won-Sik
authors: WS
authors: Yeo
authors: Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest,Gary, Indiana, United States of America.
authors: Taeok
authors: T
authors: Bae
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins; D015153:Blotting, Western; D005434:Flow Cytometry; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000382:microbiology; D016133:Polymerase Chain Reaction; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D013203:Staphylococcal Infections / Q000235:genetics / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D011494:Protein Kinases; C527351:SaeS protein, Staphylococcus aureus