ABSTRACT
Several herpesviruses encode Fc receptors that may play a role in preventing antibody-mediated clearance of the virus in vivo. Human cytomegalovirus (HCMV) induces an Fc-binding activity in cells upon infection, but the gene that encodes this Fc-binding protein has not been identified. Here, we demonstrate that the HCMV AD169 open reading frame TRL11 and its identical copy, IRL11, encode a type I membrane glycoprotein that possesses IgG Fc-binding capabilities.
Subject(s)
Carrier Proteins/genetics , Cytomegalovirus/genetics , Immunoglobulin Fc Fragments/metabolism , Immunoglobulin G/metabolism , Open Reading Frames , Amino Acid Sequence , Carrier Proteins/chemistry , Molecular Sequence Data , Molecular WeightABSTRACT
The bioluminescent marine bacterium Vibrio harveyi controls light production (lux) by an elaborate quorum-sensing circuit. V. harveyi produces and responds to two different autoinducer signals (AI-1 and AI-2) to modulate the luciferase structural operon (luxCDABEGH) in response to changes in cell-population density. Unlike all other Gram-negative quorum-sensing organisms, V. harveyi regulates quorum sensing using a two-component phosphorylation-dephosphorylation cascade. Each autoinducer is recognized by a cognate hybrid sensor kinase (called LuxN and LuxQ). Both sensors transduce information to a shared phosphorelay protein called LuxU, which in turn conveys the signal to the response regulator protein LuxO. Phospho-LuxO is responsible for repression of luxCDABEGH expression at low cell density. In the present study, we demonstrate that LuxO functions as an activator protein via interaction with the alternative sigma factor, sigma54 (encoded by rpoN). Our results suggest that LuxO, together with sigma54, activates the expression of a negative regulator of luminescence. We also show that phenotypes other than lux are regulated by LuxO and sigma54, demonstrating that in Vibrio harveyi, quorum sensing controls multiple processes.
Subject(s)
Bacterial Proteins/metabolism , DNA-Binding Proteins , DNA-Directed RNA Polymerases/metabolism , Repressor Proteins/metabolism , Sigma Factor/metabolism , Transcription Factors , Vibrio/physiology , Amino Acid Sequence , Bacterial Proteins/genetics , Binding Sites , Cloning, Molecular , DNA-Directed RNA Polymerases/genetics , Enzyme Activation , Molecular Sequence Data , Mutagenesis , Phenotype , RNA Polymerase Sigma 54 , Repressor Proteins/genetics , Sigma Factor/genetics , Vibrio/genetics , Vibrio/metabolismABSTRACT
The bioluminescent marine bacterium Vibrio harveyi controls light production using two parallel quorum-sensing systems. V. harveyi produces two autoinducers (AI-1 and AI-2), which are recognized by cognate membrane-bound two-component hybrid sensor kinases called LuxN and LuxQ respectively. Under conditions of low cell density, in the absence of autoinducer, the hybrid sensors are kinases, and under conditions of high cell density, in the presence of autoinducer, the sensors are phosphatases. These activities allow LuxN and LuxQ to modulate the level of phosphorylation of the response regulator protein LuxO. LuxO, in turn, controls the transcription of the genes encoding luciferase. The phosphorelay protein LuxU is required for signalling to LuxO. In this report, we present a genetic analysis of the activities of the AI-1 sensor LuxN. Point mutations and in frame deletions were constructed in luxN and recombined onto the chromosome of V. harveyi for in vivo phenotypic analysis. We show that the conserved histidine (H471) in the sensor kinase domain of LuxN is required for kinase activity but not for phosphatase activity. In contrast, the conserved aspartate (D771) in the response regulator domain of LuxN is required for both activities. Furthermore, the LuxN phosphatase activity is localized to the response regulator domain. Our results indicate that the LuxN kinase activity is regulated by the presence of AI-1, whereas the LuxN phosphatase activity is constitutive. We also show that signalling from the two V. harveyi quorum-sensing systems is not equivalent. AI-1 and LuxN have a much greater effect on the level of LuxO phosphate and therefore Lux expression than do AI-2 and LuxQ.
