Novel Tat-Dependent Protein Secretion

Abstract

The transcription initiation signal elicited by the binding of ferric citrate to the outer membrane FecA protein is transmitted by the FecR protein across the cytoplasmic membrane to the FecI extracytoplasmic function (ECF) sigma factor. In this issue of Journal of Bacteriology, I. J. Passmore, J. M. Dow, F. Coll, J. Cuccui, et al. (J Bacteriol 202:e00541-19, 2020, https://doi.org/10.1128/JB.00541-19) report that the FecR sequence contains both the twin-arginine signal motif and the secretory (Sec) avoidance motif typical of proteins secreted by the twin-arginine translocation (TAT) system. The same study shows that FecR is indeed secreted by Tat and represents a new class of bitopic Tat-dependent membrane proteins.

The Escherichia coli S2P intramembrane protease RseP regulates ferric citrate uptake by cleaving the sigma factor regulator FecR

“…FecR is a single-spanning cytoplasmic membrane protein of type II topology, similar to other RseP substrates, and has been reported to be processed into several fragments in vivo ( 62 , 63 ). In addition, its N-terminal cytoplasmic region has been suggested to exhibit an activity (“pro-sigma” activity) that is required for the function of FecI ( 40 , 43 ). These facts led us to examine the possibility that FecR is cleaved by RseP to activate FecI.…”

“…The Fec proteins constitute the Fec system that mediates the uptake of ferric citrate by a cell ( 34 , 35 ). We demonstrated that FecR receives sequential processing at the membrane and that RseP plays an essential role in the activation of FecI, an alternative sigma factor dedicated to the transcription of the fec operon ( 36 , 37 , 38 , 39 ), through the regulated intramembrane cleavage of a periplasmically processed form of FecR, the regulator of the fec operon expression ( 40 , 41 , 42 ), which produces the N-terminal cytoplasmic tail fragment of FecR having a “pro-sigma” activity ( 40 , 43 ) as the last step in the sequential processing of FecR at the membrane. These results uncover the details of the FecR processing in the ferric citrate–induced TM signaling and a new physiological role of RseP in the iron uptake in response to the environmental conditions in E. coli .…”

Escherichia coliS2P family intramembrane protease RseP is engaged in the regulated sequential cleavages of FecR in the ferric citrate signaling

“…FecR is a single-spanning cytoplasmic membrane protein of type II topology, similar to other RseP substrates, and has been reported to be processed into several fragments in vivo (59, 60). In addition, its N-terminal cytoplasmic region has been suggested to exhibit an activity (“pro-sigma” activity) that is required for the function of FecI (40, 43). These facts led us to examine the possibility that FecR is cleaved by RseP to activate FecI.…”

“…The Fec proteins constitute the Fec system that mediates the uptake of ferric citrate by a cell (34, 35). We demonstrated that FecR receives sequential processing at the membrane and that RseP plays an essential role in the activation of FecI, an alternative sigma factor dedicated to the transcription of the fec operon (36–39), through the regulated intramembrane cleavage of a periplasmically processed form of FecR, the regulator of the fec operon expression (40–42), which produces the N-terminal cytoplasmic tail fragment of FecR having a “pro-sigma” activity (40, 43) as the last step in the sequential processing of FecR at the membrane. These results uncover the details of the FecR processing in the ferric citrate-induced transmembrane signaling and a new physiological role of RseP in the iron uptake in response to the environmental conditions in E. coli .…”

A Review on Various Secretion Systems: A Versatile Molecular Weapon for Bacterial Pathogenesis, Special Reference to Type 7 Secretion System (T7SS) in Multi Drug Resistance Staphylococcus aureus.

“…It is used by all types of bacteria, as well as archaea, chloroplasts and plants mitochondria. In case of bacteria, Tat system exports proteins from cytoplasm across the inner cell membrane, whereas in chloroplasts, it is present in thylakoid membrane where it aids import of proteins from stroma [23,24]. That proteins have highly variability in different bacterial strains and are distributed into major types namely TatA, TatB and TatC.…”