Polarity/charge as a determinant of translocase requirements for membrane protein insertion.

The YidC insertase of Escherichia coli inserts membrane proteins with small periplasmic loops (~20 residues). However, it has difficulty transporting loops that contain positively charged residues compared to negatively charged residues and, as a result, increasing the positive charge has an increased requirement for the Sec machinery as compared to negatively charged loops (Zhu et al., 2013; Soman et al., 2014). This suggested that the polarity and charge of the periplasmic regions of membrane proteins determine the YidC and Sec translocase requirements for insertion. Here we tested this polarity/charge hypothesis by showing that insertion of our model substrate protein procoat-Lep can become YidC/Sec dependent when the periplasmic loop was converted to highly polar even in the absence of any charged residues. Moreover, adding a number of hydrophobic amino acids to a highly polar loop can decrease the Sec-dependence of the otherwise strictly Sec-dependent membrane proteins. We also demonstrate that the length of the procoat-Lep loop is indeed a determinant for Sec-dependence by inserting alanine residues that do not markedly change the overall hydrophilicity of the periplasmic loop. Taken together, the results support the polarity/charge hypothesis as a determinant for the translocase requirement for procoat insertion.

Safety evaluation of Bacillus coagulans SNZ 1969 in Wistar rats.

Bacillus coagulans SNZ 1969 is a rod-shaped, slightly acidophilic, gram-positive, spore forming and highly resilient bacteria. B. coagulans SNZ 1969 has GRAS (Generally Recognized As Safe) status for use as a probiotic in foods (US FDA number GRN-597). The present study was aimed to assess the safety of a proprietary strain Bacillus coagulans SNZ 1969 by conducting acute and sub-acute 28 days repeated dose oral toxicity studies in Wistar Rats. In the acute toxicity study, the rats were orally fed with 2000 mg/kg body weight (BW) (5 × 1011 CFU/g) of B. coagulans SNZ 1969 as a single dose to determine the LD50 values. In the sub-acute repeated dose toxicity study, six groups of experimental rats received 250, 500, 1000 mg/kgBW/day (5 × 1011 CFU/g) of the test item for 28 consecutive days. The control animals received only water. Four groups of rats were sacrificed after 28 days and the remaining two groups were kept as recovery groups and sacrificed after 42 days. The results of these study indicate that there were no treatment related changes in any of the parameters studied i.e. clinical signs, body weight, food intake, urinalysis, hematological examinations, clinical biochemistry, gross pathology and histopathology after 28 days of repeated administration. Based on the results it was concluded that the LD50 of Bacillus coagulans SNZ 1969 is more than 2000 mg/kg body weight and the NOAEL derived from this study was 1000 mg/kg/day for 28 days, this corresponds to the 5 × 1011 CFU/kg.

A prospective, randomized, double-blind, placebo-controlled, parallel-group study to evaluate the efficacy and safety of SNZ TriBac, a three-strain Bacillus probiotic blend for undiagnosed gastrointestinal discomfort.

PURPOSE: This prospective, randomized, double-blind, placebo-controlled, parallel-group study aimed to determine the efficacy and safety of a multistrain (Bacillus coagulans [SNZ 1969], Bacillus clausii [SNZ 1971], and Bacillus subtilis [SNZ 1972]) probiotic blend (SNZ TriBac) in managing symptoms of gastrointestinal (GI) discomfort in the absence of specific pathologies. METHODS: Sixty adults with symptoms of GI discomfort were enrolled (mean age, 34.89 ± 9.95 years) and randomized to receive either SNZ TriBac or placebo. Changes from baseline in Severity of Dyspepsia Assessment (SODA), Gastrointestinal Symptom Rating Scale (GSRS), and Quality of Life (QoL) scales over the course of product use were determined at baseline and on days 30 and 37 as study outcomes. RESULTS: On day 30, significant improvement with SNZ TriBac was noted in SODA burping/belching (P = 0.025), bloating (P = 0.048), sour taste (P = 0.025), and total (P = 0.007) scores as well as pain (P = 0.003), non-pain (P = 0.04), and satisfaction (P = 0.03) subscores. Significant improvement with SNZ TriBac was also observed in SODA burping/belching (P = 0.011), sour taste (P = 0.011), and total SODA scores (P < 0.001), and in SODA pain (P = 0.005), non-pain (P = 0.06), and satisfaction (P = 0.004) subscores on day 37. No adverse events were reported. CONCLUSION: Significant improvement in final SODA scores and subscores with SNZ TriBac versus placebo indicates improvement in several symptoms of gastrointestinal discomfort. This multistrain probiotic blend was well tolerated and could be an effective option for treatment of GI discomfort. TRIAL REGISTRATION: Clinical Trials Registry of India (CTRI/2018/05/014071).

YidC/Alb3/Oxa1 Family of Insertases.

The YidC/Alb3/Oxa1 family functions in the insertion and folding of proteins in the bacterial cytoplasmic membrane, the chloroplast thylakoid membrane, and the mitochondrial inner membrane. All members share a conserved region composed of five transmembrane regions. These proteins mediate membrane insertion of an assorted group of proteins, ranging from respiratory subunits in the mitochondria and light-harvesting chlorophyll-binding proteins in chloroplasts to ATP synthase subunits in bacteria. This review discusses the YidC/Alb3/Oxa1 protein family as well as their function in membrane insertion and two new structures of the bacterial YidC, which suggest a mechanism for membrane insertion by this family of insertases.

The role of the strictly conserved positively charged residue differs among the Gram-positive, Gram-negative, and chloroplast YidC homologs.

Recently, the structure of YidC2 from Bacillus halodurans revealed that the conserved positively charged residue within transmembrane segment one (at position 72) is located in a hydrophilic groove that is embedded in the inner leaflet of the lipid bilayer. The arginine residue was essential for the Bacillus subtilis SpoIIIJ (YidC1) to insert MifM and to complement a SpoIIIJ mutant strain. Here, we investigated the importance of the conserved positively charged residue for the function of the Escherichia coli YidC, Streptococcus mutans YidC2, and the chloroplast Arabidopsis thaliana Alb3. Like the Gram-positive B. subtilis SpoIIIJ, the conserved arginine was required for functioning of the Gram-positive S. mutans YidC2 and was necessary to complement the E. coli YidC depletion strain and to promote insertion of a YidC-dependent membrane protein synthesized with one but not two hydrophobic segments. In contrast, the conserved positively charged residue was not required for the E. coli YidC or the A. thaliana Alb3 to functionally complement the E. coli YidC depletion strain or to promote insertion of YidC-dependent membrane proteins. Our results also show that the C-terminal half of the helical hairpin structure in cytoplasmic loop C1 is important for the activity of YidC because various deletions in the region either eliminate or impair YidC function. The results here underscore the importance of the cytoplasmic hairpin region for YidC and show that the arginine is critical for the tested Gram-positive YidC homolog but is not essential for the tested Gram-negative and chloroplast YidC homologs.

Polarity and charge of the periplasmic loop determine the YidC and sec translocase requirement for the M13 procoat lep protein.

During membrane biogenesis, the M13 procoat protein is inserted into the lipid bilayer in a strictly YidC-dependent manner with both the hydrophobic signal sequence and the membrane anchor sequence promoting translocation of the periplasmic loop via a hairpin mechanism. Here, we find that the translocase requirements can be altered for PClep in a predictable manner by changing the polarity and charge of the peptide region that is translocated across the membrane. When the polarity of the translocated peptide region is lowered and the charged residues in this region are removed, translocation of this loop region occurs largely by a YidC- and Sec-independent mechanism. When the polarity is increased to that of the wild-type procoat protein, the YidC insertase is essential for translocation. Further increasing the polarity, by adding charged residues, switches the insertion pathway to a YidC/Sec mechanism. Conversely, we find that increasing the hydrophobicity of the transmembrane segments of PClep can decrease the translocase requirement for translocation of the peptide chain. This study provides a framework to understand why the YidC and Sec machineries exist in parallel and demonstrates that the YidC insertase has a limited capacity to translocate a peptide chain on its own.