The global public health burden of bacterial antimicrobial resistance (AMR) is intensified by Gram-negative bacteria,
which have an additional membrane, the outer membrane (OM), outside of the peptidoglycan (PG) cell wall. Bacterial twocomponent
systems (TCSs) aid in maintaining envelope integrity through a phosphorylation cascade by controlling gene
expression through sensor kinases and response regulators. In Escherichia coli, the major TCSs defending cells from envelope
stress and adaptation are Rcs and Cpx, which are aided by OM lipoproteins RcsF and NlpE as sensors, respectively. In
this review, we focus on these two OM sensors. β-Barrel assembly machinery (BAM) inserts transmembrane OM proteins
(OMPs) into the OM. BAM co-assembles RcsF, the Rcs sensor, with OMPs, forming the RcsF-OMP complex. Researchers
have presented two models for stress sensing in the Rcs pathway. The first model suggests that LPS perturbation stress
disassembles the RcsF-OMP complex, freeing RcsF to activate Rcs. The second model proposes that BAM cannot assemble
RcsF into OMPs when the OM or PG is under specific stresses, and thus, the unassembled RcsF activates Rcs. These two
models may not be mutually exclusive. Here, we evaluate these two models critically in order to elucidate the stress sensing
mechanism. NlpE, the Cpx sensor, has an N-terminal (NTD) and a C-terminal domain (CTD). A defect in lipoprotein trafficking
results in NlpE retention in the inner membrane, provoking the Cpx response. Signaling requires the NlpE NTD, but
not the NlpE CTD; however, OM-anchored NlpE senses adherence to a hydrophobic surface, with the NlpE CTD playing
a key role in this function.
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The Chikungunya virus (CHIKV) belongs to the Alphavirus
genus of Togaviridae family and contains a positive-sense
single stranded RNA genome. Infection by this virus mainly
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pain that can last for several months or years. CHIKV, a mosquito-
borne arbovirus, is considered a re-emerging pathogen
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the evaluation of prophylactic vaccines or antivirals
has been substantially hampered. In this study, we first identified
the whole structural polyprotein sequence of a CHIKV
strain isolated in South Korea (KNIH/2009/77). Phylogenetic
analysis showed that this sequence clustered within the East/
Central/South African CHIKV genotype. Using this sequence
information, we constructed a CHIKV-pseudotyped lentivirus
expressing the structural polyprotein of the Korean
CHIKV isolate (CHIKVpseudo) and dual reporter genes of
green fluorescence protein and luciferase. We then developed
a pseudovirus-based neutralization assay (PBNA) using
CHIKVpseudo. Results from this assay compared to those
from the conventional plaque reduction neutralization test
showed that our PBNA was a reliable and rapid method to
evaluate the efficacy of neutralizing antibodies. More importantly,
the neutralizing activities of human sera from CHIKVinfected
individuals were quantitated by PBNA using CHIKVpseudo.
Taken together, these results suggest that our PBNA
for CHIKV may serve as a useful and safe method for testing
the neutralizing activity of antibodies against CHIKV
in BSL-2 facilities.
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