Desolvation of the substrate-binding protein TauA dictates ligand specificity for the alkanesulfonate ABC importer TauABC

Abstract

Under limiting sulfur availability, bacteria can assimilate sulfur from alkanesulfonates. Bacteria utilize ATP-binding cassette (ABC) transporters to internalise them for further processing to release sulfur. In gram-negative bacteria the TauABC and SsuABC ensure internalization, although, these two systems have common substrates, the former has been characterized as a taurine specific system. TauA and SsuA are substrate-binding proteins (SBPs) that bind and bring the alkanesulfonates to the ABC importer for transport. Here, we have determined the crystal structure of TauA and have characterized its thermodynamic binding parameters by isothermal titration calorimetry in complex with taurine and different alkanesulfonates. Our structures revealed that the coordination of the alkanesulfonates is conserved, with the exception of Asp205 that is absent from SsuA, but the thermodynamic parameters revealed a very high enthalpic penalty cost for binding of the other alkanesulfonates relative to taurine. Our molecular dynamic simulations indicated that the different levels of hydration of the binding site contributed to the selectivity for taurine over the other alkanesulfonates. Such selectivity mechanism is very likely to be employed by other SBPs of ABC transporters.

Discovery and structure of a widespread bacterial ABC transporter specific for ergothioneine

“…A G244F substitution mutant of EgtU binds ET ≈100-fold more weakly than wild-type EgtU SBD, with strongly perturbed thermodynamics (Fig. 3b); consistent with an important role of these water molecules in organizing the ET binding site, a finding previously observed in some other QAC-specific SBPs 67,70 . Two other substitutions that target conserved residues Y419 and F293 give rise to somewhat smaller perturbations of the binding energetics and affinity.…”

“…3a, Table 1). These thermodynamic parameters are similar to those previously found for a taurine-specific SBP 70 , with an enthalpic driving force consistent with trimethylamine cation-π interactions found in osmoprotectant SBP-ligand complexes 60,62 . A G244F substitution mutant of EgtU binds ET ≈100-fold more weakly than wild-type EgtU SBD, with strongly perturbed thermodynamics (Fig.…”

The sulfoquinovosyl glycerol binding protein SmoF binds and accommodates plant sulfolipids

“…We next studied whether sulfonate binding pockets were conserved across SmoF homologues as well as other sulfonate-targeting solute binding proteins. Thus, we included SsuA from E. coli and Xanthomonas citri ( Beale et al., 2010 ; Tófoli De Araújo et al., 2013 ) and the taurine-binding protein TauA from E. coli ( Qu et al., 2019 ), which are solute-binding proteins associated with ABC transporters that bind assorted alkanesulfonates. We also included MalE as a well-characterized SBP that binds a non-sulfonated ligand.…”

Franconibacter sp., 1MS: A New Strain in Decolorization and Degradation of Azo Dyes Ponceau S Red and Methyl Orange

“…Methyl Orange and Ponceau S Red are sulfonated reactive dyes whose degradation products include sulfonated and unsulfonated aromatic amines, which are an important group of environmental pollutants that are toxic in nature. 46,47 Our study identified the compounds by GC−MS: N,Ndimethylbenzyl-1,4-diamine, sulfonamide, 1,4-diaminobenzene, 2,5-diaminobenzenesulfonic acid, and 1-amino-2 naphthol as intermediates in the degradation pathway of both dyes, which are not only highly toxic as it is evidenced in Table 2 but also able to be converted through metabolic activation into mutagenic, carcinogenic, and/ or teratogenic species as is indicated by Qu et al 48 Franconibacter sp., 1MS could be inhibited by these intermediaries and not finish the detoxification, indicating that degradation products were still toxic in some cases of the original dye as emphasized by Rawat et al 49 and Bergsten-Torralba et al 50 According to Kalyani et al, 51 it is of great concern to evaluate the phytotoxicity and microbial toxicity of the dye before and after degradation, given the use of untreated and treated textile effluents that are reported in the agricultural area, and its direct impact on soil fertility. Furthermore, effluents from untreated textiles can cause serious health and environmental risks.…”

“…Decolorization Assay. Dye decolorization was studied using the one-factor optimization approach: The influence of various culture conditions such as pH (3, 5, 7, 9, and 11), temperature (20,37,40,45, and 50 °C), the time of incubation (24,48,72,96, and 120 h), and concentration (50, 100, 200, 300, 400, 500, 600, 800, and 1000 mg/L) of dyes on the rate of decolorization was studied. When investigating one of these factors, all others were kept constant.…”