A TatABC-Type Tat Translocase Is Required for Unimpaired Aerobic Growth of Corynebacterium glutamicum ATCC13032

Abstract

The twin-arginine translocation (Tat) system transports folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of plant chloroplasts. Escherichia coli and other Gram-negative bacteria possess a TatABC-type Tat translocase in which each of the three inner membrane proteins TatA, TatB, and TatC performs a mechanistically distinct function. In contrast, low-GC Gram-positive bacteria, such as Bacillus subtilis, use a TatAC-type minimal Tat translocase in which the TatB function is carried out by a bifunctional TatA. In high-GC Gram-positive Actinobacteria, such as Mycobacterium tuberculosis and Corynebacterium glutamicum, tatA, tatB, and tatC genes can be identified, suggesting that these organisms, just like E. coli, might use TatABC-type Tat translocases as well. However, since contrary to this view a previous study has suggested that C. glutamicum might in fact use a TatAC translocase with TatB only playing a minor role, we reexamined the requirement of TatB for Tat-dependent protein translocation in this microorganism. Under aerobic conditions, the misassembly of the Rieske iron-sulfur protein QcrA was identified as a major reason for the severe growth defect of Tat-defective C. glutamicum mutant strains. Furthermore, our results clearly show that TatB, besides TatA and TatC, is strictly required for unimpaired aerobic growth. In addition, TatB was also found to be essential for the secretion of a heterologous Tat-dependent model protein into the C. glutamicum culture supernatant. Together with our finding that expression of the C. glutamicum TatB in an E. coli ΔtatB mutant strain resulted in the formation of an active Tat translocase, our results clearly indicate that a TatABC translocase is used as the physiologically relevant functional unit for Tat-dependent protein translocation in C. glutamicum and, most likely, also in other TatB-containing Actinobacteria.

The DyP-type peroxidase DtpA is a Tat-substrate required for GlxA maturation and morphogenesis in Streptomyces

“…The addition of Cu also stimulated aerial growth in the tatB mutant, but this appears to be unrelated to the maturation status of GlxA. Given that in organisms that have a TatB protein it is also required for efficient Tat-mediated translocation [ 68 – 70 ], we suspect that, like in tatA and tatC mutants, DtpA is also not secreted in tatB mutants. However, besides its role in protein translocation, TatB may have an additional function, which is not shared with TatA and TatC.…”

Arginine-deprivation–induced oxidative damage sterilizes Mycobacterium tuberculosis

“…Another potential explanation is altered protein synthesis and secretion due to the indispensability of arginine for the twin-arginine transport (TAT) secretion signal motif "RR." TAT effectors are involved in respiration, nutrition uptake, and envelope maintenance (30)(31)(32). Defects in the TAT system are associated with cell death and envelope and oxidative stress susceptibility in many bacterial pathogens including Mtb (30,31).…”

Signal peptides for recombinant protein secretion in bacterial expression systems

“…This alternative export pathway has been named the twin-arginine translocation (or Tat) pathway due to the presence of a twin-arginine pair that is present in the signal peptides of the respective Tat substrates [ 22 ]. The Tat translocase consists of the components TatA, TatB, and TatC in Gram-negative bacteria and Gram-positive bacteria with a high GC-content, whereas a minimal translocase consisting solely of TatA and TatC is operating in Gram-positive bacteria with a low GC-content [ 23 – 25 ]. In the latter case, the TatA protein is bifunctional and, besides the TatA functions, also takes over the role of TatB [ 26 , 27 ].…”