A highly active bile salt hydrolase from Enterococcus faecalis shows positive cooperative kinetics

Sanye tablet regulates gut microbiota and bile acid metabolism to attenuate hepatic steatosis

ETHNOPHARMACOLOGICAL RELEVANCE

Sanye Tablet (SYT), a patent traditional Chinese prescription, is commonly used in treating type 2 diabetes mellitus and hyperlipidemia. Both clinical and animal studies suggest that SYT effectively regulates lipid metabolism. However, its mode of action on hepatic steatosis has yet to be fully elucidated.

AIM OF STUDY

This study investigates the lipid-regulating effects and underlying mechanism of SYT in high-fat diet (HFD)-induced hepatic steatosis mice.

MATERIAL AND METHODS

The inhibitory effects of SYT on developing hepatic steatosis were investigated in HFD-fed C57BL/6N mice. Biochemical markers, including total cholesterol (TC) and triglycerides (TG), were measured using specific kits. Hepatic histological alterations were determined by Hematoxylin and Eosin (H&E) and Oil Red O staining. Hepatic, fecal, and systemic bile acids (BAs) profiles were detected by UPLC-MS. mRNA and protein levels of BAs synthesis-related enzymes and critical nodes of farnesoid X receptor (FXR)/fibroblast growth factor 15 (FGF15)/fibroblast growth factor receptor 4 (FGFR4) signaling were detected. Fecal microbial composition was analyzed by 16S rRNA gene sequencing and the antimicrobial activity of SYT was further evaluated in vitro.

RESULTS

SYT alleviated HFD-induced hepatic steatosis by decreasing TG and TC levels, relieving hepatocyte ballooning, and promoting hepatic BAs synthesis. Moreover, SYT significantly increased the levels of taurine-conjugated BAs in the liver and feces, which in turn inhibited the FXR/FGF15/FGFR4 signaling. Consequently, the hepatic BAs synthesis-related enzyme expression was promoted to reduce lipid accumulation. Notably, SYT remodeled the gut microbiota composition of HFD-fed mice, especially inhibiting the growth of bile salt hydrolase (BSH)-producing bacteria, such as Lactobacillus murinus, Lactobacillus johnsonii, and Enterococcus faecalis.

CONCLUSION

The findings illustrated that SYT prevented hepatic steatosis by improving hepatic lipid accumulation, which is reflected in modulating the gut-liver axis. SYT corrects BAs profile, restores perturbed FXR/FGF15/FGFR4 signaling and promotes hepatic BAs synthesis, which is associated with modulation on certain BSH-producing bacteria.

Review on the Function, Substrate Affinity, and Potential Application of Bile Salt Hydrolase Originated from Probiotic Strains of Lactobacillus, Bifidobacterium, and Enterococcus

Bile salt hydrolase (BSH: EC.3.5.1.24) has been used as a biomarker for probiotics for an extended period. It is mostly present in the gut environment of vertebrates. Additionally, it influences the viability of probiotics. This biomarker is considered a promising nutritional supplement due to its unique ability to effectively address elevated blood cholesterol levels, a common issue in modern society. However, the commercialization of BSH has been limited by an incomplete understanding of the intestinal microbiota and the function of BSH. Hence, in this review, we aim to reveal the current advancements in BSH research and outline the necessary areas of investigation for future studies. The review highlights key findings related to the substrate affinity of BSH in probiotic bacteria and its BSH gene phylogeny that have been researched until today, suggesting further research regarding the differences in multiple BSH genes and corresponding differences in BSH affinity.

Targeted Assay Engineering Enhances Bile Salt Hydrolase Activity in Heyndrickxia coagulans ATCC 7050 and Lactiplantibacillus plantarum ATCC 10012

The recent emergence of bile salt hydrolase (BSH) enzyme as a therapeutic target reflects its unbound potential in mitigating hypercholesterolemia, obesity, and gastrointestinal issues. However, to bolster its industrial application, optimization of BSH assay lays the cornerstone for enhancing sensitivity, specificity, and reproducibility. The current study delved into optimizing the BSH assay parameters utilizing response surface methodology (RSM) and one-factor-at-a-time (OFAT) method for two novel, natural BSH producers, Heyndrickxia coagulans ATCC 7050 and Lactiplantibacillus plantarum ATCC 10012. Factors such as pH, temperature, cell concentration, and substrate concentration were optimized using RSM and numerical optimization. The analysis of responses unveiled significant insights into the biochemical characteristics of BSH from both organisms. The optimal pH for BSH activity from H. coagulans ATCC 7050 and L. plantarum ATCC 10012 was determined to be 6.1 and 6.0, with their corresponding optimal temperatures being 60 °C and 40 °C, respectively. Subsequent to RSM, optimization of the remaining parameters such as buffer type, buffer molarity, cells-to-substrate ratio, etc., performed using the classical OFAT approach further enhanced BSH activity, with H. coagulans ATCC 7050 and L. plantarum ATCC 10012 exhibiting a 1.45 and 0.87-fold increase, respectively. Conventionally, even though BSH has been optimized using the OFAT approach, this is the first instance in which a hybrid model using RSM has been applied to achieve a greater performance. These findings offer valuable insights in augmenting the specificity, efficiency, and stability of BSH and broaching new avenues for industrial and therapeutic applications.

Gut microbiota and bile acids: Metabolic interactions and impacts on diabetic kidney disease

The intestinal microbiota comprises approximately 1013-1014 species of bacteria and plays a crucial role in host metabolism by facilitating various chemical reactions. Secondary bile acids (BAs) are key metabolites produced by gut microbiota.Initially synthesized by the liver, BA undergoes structural modifications through the activity of various intestinal microbiota enzymes, including eukaryotic, bacterial, and archaeal enzymes. These modified BA then activate specific receptors that regulate multiple metabolic pathways in the host, such as lipid and glucose metabolism, energy balance, inflammatory response, and cell proliferation and death. Recent attention has been given to intestinal flora disorders in diabetic kidney disease (DKD), where activation of BA receptors has shown promise in alleviating diabetic kidney damage by modulating renal lipid metabolism and mitochondrial production. Imbalances in the intestinal flora can influence the progression of DKD through the regulation of bile acid and its receptor pathways. This review aims to propose a mechanism involving the gut-BA-diabetes and nephropathy axes with the goal of optimizing new strategies for treating DKD.

Structural and functional analysis of a bile salt hydrolase from the bison microbiome

The bile salt hydrolases (BSHs) are significant constituents of animal microbiomes. An evolving appreciation of their roles in health and disease has established them as targets of pharmacological inhibition. These bacterial enzymes belong to the N-terminal nucleophile superfamily and are best known to catalyze the deconjugation of glycine or taurine from bile salts to release bile acid substrates for transformation and or metabolism in the gastrointestinal tract. Here, we identify and describe the BSH from a common member of the Plains bison microbiome, Arthrobacter citreus (BSHAc). Steady-state kinetic analyses demonstrated that BSHAc is a broad-spectrum hydrolase with a preference for glycine-conjugates and deoxycholic acid (DCA). Second-order rate constants (kcat/KM) for BSHAc-catalyzed reactions of relevant bile salts-glyco- and tauro-conjugates of cholic acid and DCA- varied by ∼30-fold and measured between 1.4 × 105 and 4.3 × 106 M-1s-1. Interestingly, a pan-BSH inhibitor named AAA-10 acted as a slow irreversible inhibitor of BSHAc with a rate of inactivation (kinact) of ∼2 h-1 and a second order rate constant (kinact/KI) of ∼24 M-1s-1 for the process. Structural characterization of BSHAc reacted with AAA-10 showed covalent modification of the N-terminal cysteine nucleophile, providing molecular details for an enzyme-stabilized product formed from this mechanism-based inhibitor's α-fluoromethyl ketone warhead. Structural comparison of the BSHs and BSH:inhibitor complexes highlighted the plasticity of the steroid-binding site, including a flexible loop that is variable across well-studied BSHs.

Gut-Liver-Pancreas Axis Crosstalk in Health and Disease: From the Role of Microbial Metabolites to Innovative Microbiota Manipulating Strategies

The functions of the gut are closely related to those of many other organs in the human body. Indeed, the gut microbiota (GM) metabolize several nutrients and compounds that, once released in the bloodstream, can reach distant organs, thus influencing the metabolic and inflammatory tone of the host. The main microbiota-derived metabolites responsible for the modulation of endocrine responses are short-chain fatty acids (SCFAs), bile acids and glucagon-like peptide 1 (GLP-1). These molecules can (i) regulate the pancreatic hormones (insulin and glucagon), (ii) increase glycogen synthesis in the liver, and (iii) boost energy expenditure, especially in skeletal muscles and brown adipose tissue. In other words, they are critical in maintaining glucose and lipid homeostasis. In GM dysbiosis, the imbalance of microbiota-related products can affect the proper endocrine and metabolic functions, including those related to the gut-liver-pancreas axis (GLPA). In addition, the dysbiosis can contribute to the onset of some diseases such as non-alcoholic steatohepatitis (NASH)/non-alcoholic fatty liver disease (NAFLD), hepatocellular carcinoma (HCC), and type 2 diabetes (T2D). In this review, we explored the roles of the gut microbiota-derived metabolites and their involvement in onset and progression of these diseases. In addition, we detailed the main microbiota-modulating strategies that could improve the diseases' development by restoring the healthy balance of the GLPA.

Electrostatic Interactions Dictate Bile Salt Hydrolase Substrate Preference

The human intestines are colonized by trillions of microbes, comprising the gut microbiota, which produce diverse small molecule metabolites and modify host metabolites, such as bile acids, that regulate host physiology. Biosynthesized in the liver, bile acids are conjugated with glycine or taurine and secreted into the intestines, where gut microbial bile salt hydrolases (BSHs) deconjugate the amino acid to produce unconjugated bile acids that serve as precursors for secondary bile acid metabolites. Among these include a recently discovered class of microbially conjugated bile acids (MCBAs), wherein alternative amino acids are conjugated onto bile acids. To elucidate the metabolic potential of MCBAs, we performed detailed kinetic studies to investigate the preference of BSHs for host-conjugated bile acids and MCBAs. We identified a BSH that exhibits positive cooperativity uniquely for MCBAs containing an aromatic side chain. Further molecular modeling and phylogenetic analyses indicated that the BSH preference for aromatic MCBAs is due to a substrate-specific cation-π interaction and is predicted to be widespread among human gut microbial BSHs.

Electrostatic Interactions Dictate Bile Salt Hydrolase Substrate Preference

The human intestines are colonized by trillions of microbes, comprising the gut microbiota, which produce diverse small molecule metabolites and modify host metabolites, such as bile acids, that regulate host physiology. Biosynthesized in the liver, bile acids are conjugated with glycine or taurine and secreted into the intestines, where gut microbial bile salt hydrolases (BSHs) deconjugate the amino acid to produce unconjugated bile acids that serve as precursors for secondary bile acid metabolites. Among these include a recently discovered class of microbially-conjugated bile acids (MCBAs), wherein alternative amino acids are conjugated onto bile acids. To elucidate the metabolic potential of MCBAs, we performed detailed kinetic studies to investigate the preference of BSHs for host- and microbially-conjugated bile acids. We identified a BSH that exhibits positive cooperativity uniquely for MCBAs containing an aromatic sidechain. Further molecular modeling and phylogenetic analyses indicated that BSH preference for aromatic MCBAs is due to a substrate-specific cation-π interaction and is predicted to be widespread among human gut microbial BSHs.

Probiotic characteristics of Lactobacillus gasseri TF08-1: A cholesterol-lowering bacterium, isolated from human gut

Lactobacillus contribute to maintain the human healthy and use for nutritional additives as probiotics. In this study, a cholesterol-lowering bacterium, Lactobacillus gasseri TF08-1, was isolated from the feces of a healthy adolescent, and its probiotic potentials were evaluated through genomic mining and in vitro test. The assembled draft genome comprised of 1,974,590 bp and was predicted total of 1,940 CDSs. The annotation of the genome revealed that L. gasseri TF08-1 harbored abundant categories of functional genes in metabolic and information processing. Moreover, strain TF08-1 has capacity to utilize D-Glucose, Sucrose, D-Maltose, Salicin, D-Xylose, D-Cellobiose, D-Mannose, and D-Trehalose, as the carbon source. The safety assessment showed strain TF08-1 contained few antibiotic resistance genes and virulence factors and was only resistant to 2 antibiotics detected by antimicrobial susceptibility test. A high bile salt hydrolase activity was found and a cholesterol-reducing effect was determined in vitro, which the result showed a remarkable cholesterol removal capability of L. gasseri TF08-1 with an efficiency of 84.40 %. This study demonstrated that the strain showed great capability of exopolysaccharide production, and tolerance to acid and bile salt. Therefore, these results indicate that L. gasseri TF08-1 can be considered as a safe candidate for probiotic, especially its potential in biotherapeutic for metabolic diseases.

Chemical proteomic analysis of bile acid-protein targets in Enterococcus faecium

Bile acids are important gut microbiota metabolites that regulate both host and microbial functions. To identify the direct protein targets of bile acids in Enterococcus, we synthesized and validated the activity of a lithocholic acid (LCA) photoaffinity reporter, x-alk-LCA-3. Chemical proteomics of x-alk-LCA-3 in E. faecium Com15 reveals many candidate LCA-interacting proteins, which are involved in cell well synthesis, transcriptional regulation and metabolism. To validate the utility of bile acid photoaffinity labeling, we characterized a putative bile salt hydrolase (BSH) crosslinked by x-alk-LCA-3, and demonstrated that this BSH was effective in converting taurolithocholic acid (TLCA) to LCA in E. faecium and in vitro. Chemical proteomics should afford new opportunities to characterize bile acid-protein targets and mechanisms of action in the future.

Bile acid metabolism and signaling, the microbiota, and metabolic disease

The diversity, composition, and function of the bacterial community inhabiting the human gastrointestinal tract contributes to host health through its role in producing energy or signaling molecules that regulate metabolic and immunologic functions. Bile acids are potent metabolic and immune signaling molecules synthesized from cholesterol in the liver and then transported to the intestine where they can undergo metabolism by gut bacteria. The combination of host- and microbiota-derived enzymatic activities contribute to the composition of the bile acid pool and thus there can be great diversity in bile acid composition that depends in part on the differences in the gut bacteria species. Bile acids can profoundly impact host metabolic and immunological functions by activating different bile acid receptors to regulate signaling pathways that control a broad range of complex symbiotic metabolic networks, including glucose, lipid, steroid and xenobiotic metabolism, and modulation of energy homeostasis. Disruption of bile acid signaling due to perturbation of the gut microbiota or dysregulation of the gut microbiota-host interaction is associated with the pathogenesis and progression of metabolic disorders. The metabolic and immunological roles of bile acids in human health have led to novel therapeutic approaches to manipulate the bile acid pool size, composition, and function by targeting one or multiple components of the microbiota-bile acid-bile acid receptor axis.

Discovery and characterization of amentoflavone as a naturally occurring inhibitor against the bile salt hydrolase produced by Lactobacillus salivarius

Bile salt hydrolases (BSHs), a group of cysteine-hydrolases produced by gut microbes, play a crucial role in the hydrolysis of glycine- or taurine-conjugated bile acids and have been validated as key targets to modulate bile acid metabolism. This study aims to discover one or more efficacious inhibitors against a BSH produced by Lactobacillus salivarius (lsBSH) from natural products and to characterize the mechanism of the newly identified BSH inhibitor(s). Following screening of the inhibition potentials of more than 100 natural compounds against lsBSH, amentoflavone (AMF), a naturally occurring biflavone isolated from various medicinal plants, was discovered to be an efficacious BSH inhibitor (IC50 = 0.34 μM). Further investigation showed that AMF could strongly inhibit the lsBSH-catalyzed hydrolytic reaction in living gut microbes. Inhibition kinetic analyses demonstrated that AMF reversibly inhibited the lsBSH-catalyzed hydrolytic reaction in a mixed-inhibition manner, with an apparent Ki value of 0.65 μM. Fluorescence quenching assays suggested that AMF could quench the fluorescence of lsBSH via a static quenching procedure. Docking simulations suggested that AMF could be fitted into lsBSH at two distinct ligand-binding sites, mainly via hydrophobic interactions and hydrogen bonding, which explained well the mixed inhibition mode of this agent. Animal tests showed that the hydrolytic activities of BSHs in mice feces could be significantly blocked by AMF. In summary, this study reports that AMF is a strong, naturally occurring inhibitor of lsBSH, which offers a promising lead compound to develop novel agents for modulating bile acid metabolism in the host via targeting BSHs.

The Remodeling Effects of High-Concentrate Diets on Microbial Composition and Function in the Hindgut of Dairy Cows

At present, research on high-concentrate (HC) diets mostly focused on the rumen, and there is a paucity of information on the hindgut microbiota of dairy cows. In the present study, a 2 × 2 crossover design with four healthy Holstein cows was used, and the metagenomics approach was adopted to reveal the remodeling effects of HC diets on hindgut microbiota and their metabolic functions. Results showed that, compared with the low-concentrate (LC) diets, HC diets have markedly decreased (p < 0.05) the abundance of cellulolytic bacteria (such as Fibrobacter, Ruminococcus, and Ruminiclostridium) and methanogens (such as Methanobrevibacter, Methanosarcina, and Methanosphaera); and correspondingly, HC diets have significantly reduced (p < 0.05) the abundance of carbohydrate-active enzymes (CAZy) related to hemicellulases (GH10, GH11, and GH54) and cellulases (GH1, GH44, and GH45) and increased the abundance of one oligosaccharide-degrading enzyme (GH32). Furthermore, 62 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of hindgut microbiota were affected (p < 0.05) by different dietary treatments, and the major pathways altered by HC diets were “Methane metabolism” (enriched in the LC group), “Lipid metabolism” (enriched in the HC group), and several sub-pathways in “Amino acid metabolism” (such as Phenylalanine metabolism, and Phenylalanine, tyrosine, and tryptophan biosynthesis). Also, the microbial genes involved in the pathways “Methane metabolism” (except 1 gene), “Tryptophan metabolism”, and “Phenylalanine metabolism” were all decreased (p < 0.05) in the present study. These findings suggested that HC diets caused the remodeling of hindgut microbiota and its potential functions, and these results may benefit in gaining a deeper understanding of the impact of HC diets on the hindgut microbiota of dairy cows.

Lotus seed resistant starch affects the conversion of sodium taurocholate by regulating the intestinal microbiota

We investigated the ability of lotus seed resistant starch (LRS) to affect the conversion of sodium taurocholate (STCA) by regulating the intestinal flora, using glucose (GLU) and high amylose corn starch (HAMS) as controls. The dominant microbiota in LRS group were mainly Lactobacillus and Escherichia_Shigella, with a small proportion of Bifidobacterium. Meanwhile, Lactobacillus, Bifidobacterium and Enterococcus were dominant microbiota in the HAMS group. Lactobacillus, Burkholderia-Caballeronia-Paraburkholderia and Sphingomonas were found in the GLU group. Furthermore, Bifidobacterium, Enterococcus and Escherichia_Shigella were negatively correlated with STCA and sodium taurodeoxycholate (STDCA), while these bacteria were positively correlated with bile salt hydrolase (BSH) and hydroxysteroid dehydrogenase (HSDH) content. Meanwhile Burkholderia-Caballeronia-Paraburkholderia and Sphingomonas were positively correlated with STCA and STDCA, while these bacteria were negatively correlated with BSH and HSDH content. LRS promoted the proliferation of Bifidobacterium and Escherichia_Shigella to secret more BSH and HSDH, accelerating the hydrolysis of STCA and reducing the conversion of STDCA.

The Microbiota and the Gut-Brain Axis in Controlling Food Intake and Energy Homeostasis

Obesity currently represents a major societal and health challenge worldwide. Its prevalence has reached epidemic proportions and trends continue to rise, reflecting the need for more effective preventive measures. Hypothalamic circuits that control energy homeostasis in response to food intake are interesting targets for body-weight management, for example, through interventions that reinforce the gut-to-brain nutrient signalling, whose malfunction contributes to obesity. Gut microbiota-diet interactions might interfere in nutrient sensing and signalling from the gut to the brain, where the information is processed to control energy homeostasis. This gut microbiota-brain crosstalk is mediated by metabolites, mainly short chain fatty acids, secondary bile acids or amino acids-derived metabolites and subcellular bacterial components. These activate gut-endocrine and/or neural-mediated pathways or pass to systemic circulation and then reach the brain. Feeding time and dietary composition are the main drivers of the gut microbiota structure and function. Therefore, aberrant feeding patterns or unhealthy diets might alter gut microbiota-diet interactions and modify nutrient availability and/or microbial ligands transmitting information from the gut to the brain in response to food intake, thus impairing energy homeostasis. Herein, we update the scientific evidence supporting that gut microbiota is a source of novel dietary and non-dietary biological products that may beneficially regulate gut-to-brain communication and, thus, improve metabolic health. Additionally, we evaluate how the feeding time and dietary composition modulate the gut microbiota and, thereby, the intraluminal availability of these biological products with potential effects on energy homeostasis. The review also identifies knowledge gaps and the advances required to clinically apply microbiome-based strategies to improve the gut-brain axis function and, thus, combat obesity.

Genetic and Phenotypic Characteristics of a Multi-strain Probiotic for Broilers

Bacteria isolated from different segments of the gastro-intestinal tract (GIT) of healthy free-range broilers were screened for probiotic properties. Six strains were selected and identified as Lactobacillus gallinarum, Lactobacillus johnsonii, Lactobacillus salivarius, Lactobacillus crispatus, Enterococcus faecalis and Bacillus amyloliquefaciens based on 16S rRNA, gyrB and recA gene sequence analyses. All six strains produced exopolysaccharides (EPS) and formed biofilms under conditions simulating the broiler GIT. Lactobacillus johnsonii DPN184 and L. salivarius DPN181 produced hydrogen peroxide, and L. crispatus DPN167 and E. faecalis DPN94 produced bile salt hydrolase (BSH) and phytase. Bacillus amyloliquefaciens DPN123 produced phytase, amylase, surfactin and iturin A1. No abnormalities were observed when broilers were fed the multi-strain combination, suggesting that it could be used as a probiotic.

Bile salt hydrolase activity is present in nonintestinal lactic acid bacteria at an intermediate level

It is generally considered that bile salt hydrolase (BSH) activity is hardly detected in nonintestinal lactic acid bacteria (LAB). The aim of this study was to investigate the distribution and intensity of BSH activity in LAB isolated from naturally fermented vegetables and milk. A total of 624 lactic acid bacterial strains classified into 6 genera and 50 species were isolated from 144 naturally fermented vegetable samples and 103 naturally fermented milk samples, and their BSH activity was screened by gas chromatography with electron capture detection. The BSH-positive strains were further analyzed quantitatively for their deconjugation ability against six human-conjugated bile salts by HPLC based on the disappearance of the conjugated bile salts from the reaction mixture. The results showed that 39% of the strains possessed BSH activity distributed in 24 lactic acid bacterial species. The strains of the fermented vegetable origin showed a 0.5-fold higher incidence of BSH-positive strains than those of the fermented milk origin, and the lactic acid bacilli exhibited 2.5-fold higher incidence of BSH-positive strains than the lactic acid cocci in general. The strains of the fermented vegetable origin generally had greater bile salt deconjugation ability than those of the fermented milk origin. More than 97% and 93% of the BSH-positive strains exhibited a greater substrate preference for glycoconjugated bile salts than tauroconjugated bile salts and for dihydroxy bile salts than trihydroxy bile salts, respectively. This study demonstrated that BSH activity was also present in nonintestinal LAB.

Bile salt hydrolases: Structure and function, substrate preference, and inhibitor development

The worldwide trend of limiting the use of antibiotic growth promoters (AGPs) in animal production creates challenges for the animal feed industry, thus necessitating the development of effective non-antibiotic alternatives to improve animal performance. Increasing evidence has shown that the growth-promoting effect of AGPs is highly correlated with the reduced activity of bile salt hydrolase (BSH, EC 3.5.1.24), an intestinal bacteria-producing enzyme that has a negative impact on host fat digestion and energy harvest. Therefore, BSH inhibitors may become novel, attractive alternatives to AGPs. Detailed knowledge of BSH substrate preferences and the wealth of structural data on BSHs provide a solid foundation for rationally tailored BSH inhibitor design. This review focuses on the relationship between structure and function of BSHs based on the crystal structure, kinetic data, molecular docking and comparative structural analyses. The molecular basis for BSH substrate recognition is also discussed. Finally, recent advances and future prospectives in the development of potent, safe, and cost-effective BSH inhibitors are described.

Structure and function of a highly active Bile Salt Hydrolase (BSH) from Enterococcus faecalis and post-translational processing of BSH enzymes

Bile Salt Hydrolase (BSH), a member of Cholylglycine hydrolase family, catalyzes the de-conjugation of bile acids and is evolutionarily related to penicillin V acylase (PVA) that hydrolyses a different substrate such as penicillin V. We report the three-dimensional structure of a BSH enzyme from the Gram-positive bacteria Enterococcus faecalis (EfBSH) which has manifold higher hydrolase activity compared to other known BSHs and displays unique allosteric catalytic property. The structural analysis revealed reduced secondary structure content compared to other known BSH structures, particularly devoid of an anti-parallel β-sheet in the assembly loop and part of a β-strand is converted to increase the length of a substrate binding loop 2. The analysis of the substrate binding pocket showed reduced volume owing to altered loop conformations and increased hydrophobicity contributed by a higher ratio of hydrophobic to hydrophilic groups present. The aromatic residues F18, Y20 and F65 participate in substrate binding. Thus, their mutation affects enzyme activity. Docking and Molecular Dynamics simulation studies showed effective polar complementarity present for the three hydroxyl (-OH) groups of GCA substrate in the binding site contributing to higher substrate specificity and efficient catalysis. These are unique features characteristics of this BSH enzyme and thought to contribute to its higher activity and specificity towards bile salts as well as allosteric effects. Further, mechanism of autocatalytic processing of Cholylglycine Hydrolases by the excision of an N-terminal Pre-peptide was examined by inserting different N-terminal pre-peptides in EfBSH sequence. The results suggest that two serine residues next to nucleophile cysteine are essential for autocalytic processing to remove precursor peptide. Since pre-peptide is absent in EfBSH the mutation of these serines is tolerated. This suggests that an evolution-mediated subordination of the pre-peptide excision site resulted in loss of pre-peptide in EfBSH and other related Cholylglycine hydrolases.

Importance of microbial defence systems to bile salts and mechanisms of serum cholesterol reduction

An important feature of the intestinal microbiota, particularly in the case of administered probiotic microorganisms, is their resistance to conditions in the gastrointestinal tract, particularly tolerance to and growth in the presence of bile salts. Bacteria can use several defence mechanisms against bile, including special transport mechanisms, the synthesis of various types of surface proteins and fatty acids or the production of exopolysaccharides. The ability to enzymatically hydrolyse bile salts occurs in a variety of bacteria. Choloylglycine hydrolase (EC 3.5.1.24), a bile salt hydrolase, is a constitutive intracellular enzyme responsible for the hydrolysis of an amide bond between glycine or taurine and the steroid nucleus of bile acids. Its presence was demonstrated in specific microorganisms from several bacterial genera (Lactobacillus spp., Bifidobacterium spp., Clostridium spp., Bacteroides spp.). Occurrence and gene arrangement encoding this enzyme are highly variable in probiotic microorganisms. Bile salt hydrolase activity may provide the possibility to use the released amino acids by bacteria as sources of carbon and nitrogen, to facilitate detoxification of bile or to support the incorporation of cholesterol into the cell wall. Deconjugation of bile salts may be directly related to a lowering of serum cholesterol levels, from which conjugated bile salts are synthesized de novo. Furthermore, the ability of microorganisms to assimilate or to bind ingested cholesterol to the cell wall or to eliminate it by co-precipitation with released cholic acid was also documented. Some intestinal microflora produce cholesterol reductase that catalyses the conversion of cholesterol to insoluble coprostanol, which is subsequently excreted in faeces, thereby also reducing the amount of exogenous cholesterol.