Interaction Of Bile Salts Research Articles

Volumetric, compressibility and viscometric studies on intermolecular interactions of NaC and NaDC with Emtricitabine and Lamivudine in aqueous medium at (298.15–313.15) K

Bile salts are bio-compatible natural amphiphiles having a significant role in pharmaceutical field as a solubility and permeability enhancer and possess a great biological importance for release and transport of nutrients due to dynamic micellization behavior. Hence, to unfold the interactional mystery of drug − bile salt system in the field of anti-retroviral drugs, we have aimed to investigate solute–solute and solute–solvent interactions of bile salts (NaC and NaDC) with anti-HIV drugs (Emtricitabine and Lamivudine) by using various techniques like volumetry, compressibility, and viscometry at temperature range (298.15 K-313.15 K) with a regular variation of 5 K. Experimental density and speed of sound data have been used to evaluate various physicochemical parameters such as apparent molar volume (φv), isentropic compressibility (κs), and apparent molar adiabatic compression (φκ). The CMC values of bile salts in pure water and aqueous solution of ECT and LMV at 298.15 K have also been evaluated from speed of sound data which corroborate well with our earlier conductivity study on these surfactants. The trends of φv, κs and φκ values for both NaC and NaDC with temperature and in presence of drugs (ECT/LMV) indicate strong solute–solvent interactions in studied system. The results are elucidated in terms of electrostatic and hydrophilic-hydrophobic interactions in bile salt-drug-water system which is confirmed by co-sphere overlap model. Comparatively, NaC offers strong interactions with both drugs due to more hydrophilic character than NaDC. Similarly, out of ECT and LMV, ECT shows strong solute–solvent interactions with both bile salts due to more hydrophilic character than LMV. Relative viscosity parameter (ηr) determined from viscosity measurements further supports above results. This interactional knowledge of bile salts with ECT and LMV would be beneficial to develop a better mechanism in pharmacy for enhancing efficacy and permeability of anti-HIV drugs by using bile salts as a drug delivery agent.

Conductometric and Fluorescence Probe Analysis to Investigate the Interaction between Bioactive Peptide and Bile Salts: A Micellar State Study.

The present work deals with the micellar state study of sodium cholate and sodium deoxycholate in the aqueous solution of a bioactive peptide, namely glycyl dipeptide, having different concentrations through conductivity and fluorescence methods at different temperatures. The data obtained from conductivity is plotted against the concentration of Bile salts, and CMC (critical micelle concentration) values are calculated. The results realized have been elucidated with reference to Glycyl dipeptide-bile salts hydrophobic/hydrophilic interactions existing in solution. In addition, the CMC values converted to mole fraction (Xcmc) values have been used to evaluate the standard thermodynamic factors of micellization viz., enthalpy H, free energy ΔGm0, and entropy (ΔSm0) which extract information regarding thermodynamic feasibility of micellar state, energy alteration, and the assorted interactions established in the existing (bile salts-water-glycyl dipeptide) system. Furthermore, the pyrene fluorescence spectrum has also been utilized to study the change in micro polarity induced by the interactions of bile salts with glycyl dipeptide and the aggregation action of bile salts. The decrease in modification in the ratio of intensities of first and third peaks i.e., (I1/I3) for the pyrene molecules in aqueous bile salts solution by the addition of dipeptide, demonstrates that the micelle polarity is affected by glycyl dipeptide. This ratio has also been utilized to determine CMC values for the studied system, and the results have been found to be in good correlation with observations made in conductivity studies.

A meticulous study on the interaction of bile salts with star block copolymeric micelles

Here we report, the interaction of a star block copolymer T1304 and biologically important additive, bile salts (BS) in aqueous condition. Bile salts used for the system are sodium cholate (NaC), sodium taurocholate (NaTC) and sodium deoxycholate (NaDC). Mixed micelles of T1304-BS have been assessed by employing cloud point (CP), scattering [dynamic light scattering (DLS), small-angle neutron scattering (SANS)] and spectral techniques [UV–visible, 1H NMR, and fluorescence spectroscopy]. As the system is comprising of two important bio amphiphiles, so the solubilization of drug Quercetin (QCT) in this mixed micellar environment is also studied to give it a broader spectrum. An increased trend in CP along with a decrease of micellar size is observed with the addition of BSs. With increasing concentration of bile salts, the mixed micellar aggregates are becoming surfactant rich and maximum replacement of T1304 molecule is done by NaDC due to its lower CMC and more hydrophobicity.

Mechanism of Taurohyodeoxycholate-induced Biliary Phospholipid Efflux -Understanding the Function of the ABCB4 Enhancer for Developing Therapeutic Agents against Bile Salt-induced Liver Injury

Biliary lipids primarily consist of bile salts, phospholipids, and cholesterol. Bile salts have potent detergent properties and deleterious effects on the cell membrane and are cytotoxic to hepatocytes. We have previously reported that phosphatidylcholine (PC), the predominant bile phospholipid, protects hepatocytes from the cytotoxicity of bile salts, whereas cholesterol reverses the cytoprotective effects of PC against bile salts. ABCB4, a member of the ATP-binding cassette transporter family, secretes biliary phospholipids, especially PC, from the hepatocytes into the bile. Using Abcb4 knockout mice and HEK293 cells that stably expressed ABCB4, we examined the effects of taurine- or glycine-conjugated cholate, ursodeoxycholate, and hyodeoxycholate on the ABCB4-mediated efflux of PC. We observed that the biliary secretion of PC in wild-type mice significantly increased following infusion of all the tested bile salts, especially taurohyodeoxycholate. On the other hand, the biliary secretion of PC in Abcb4 knockout mice was not affected by the bile salt infusions. The results also demonstrated that the efflux of PC from ABCB4-expressing HEK293 cells was significantly stimulated by taurohyodeoxycholate, which has a strong potential to form mixed micelles with PC. Furthermore, the results of our study emphasized the possibility that the specific interactions of bile salts with ABCB4 are necessary for the release of PC molecules from the binding pocket of ABCB4 into the aqueous environment. Further understanding of this mechanism will aid in the development of novel therapeutic agents for cholestatic liver diseases.

Synergistic activity of bile salts and their derivatives in combination with conventional antimicrobial agents against Acinetobacter baumannii

Ethnopharmacological relevanceBile traditionally was used in wound healing, having erodent, antioxidant and antimicrobial potential. Acinetobacter baumannii is a frequent etiological agent of wound infections, exhibiting high level of resistance to conventional antibiotics. Aim of the studyTo determine the effect of selected bile acid sodium salts and their 3-dehydro (i.e. 3-oxo) derivatives, as well as their combinations with commercial antibiotics against A. baumanniia, to confirm bile ethnopharmacological application in wound healing from aspect of microbiology. Materials and methodsThe sensitivity of reference and multidrug resistant (MDR) A. baumannii strains to bile salts, their derivatives and conventional antibiotics were examined by a microtiter plate method. The interaction of bile salts/derivatives and antibiotics was examined by a checkerboard method and time kill curve method. The interaction of bile salts with ciprofloxacin in terms of micelles formation was examined by DOSY NMR technique. ResultsThe bile salts sodium deoxycholate (Na-DCA) and sodium chenodeoxycholate (Na-CDCA), as well as their derivatives sodium 3-dehydro-deoxycholate (Na-3DH-DCA) and sodium 3-dehydro-chenodeoxycholate (Na-3DH-CDCA), potentiate antibiotic activity and resensitize A. baumannii. The bile salts and their derivatives enhance A. baumannii sensitivity to antibiotics, particularly those that should penetrate cell to exhibit activity. The sodium salts of bile acid derivatives, namely Na-3DH-DCA and Na-3DH-CDCA, showed synergy against both reference and MDR strain in combination with ciprofloxacin or gentamicin, while synergy with gentamicin was obtained in all combinations, regardless of bile salt type and bacterial strains. The synergy with Na-3DH-CDCA was further confirmed by the time-kill curve method, as bacterial number decreased after 12 h. NMR experiment revealed that this bile salt derivative and ciprofloxacin form co-aggregates when bile salts concentration was higher than critical micelle concentrations (CMC), which indicate the possibility that bile salts enhance ciprofloxacin cell penetration by membrane destabilization, contributing to the synergy. ConclusionThe synergistic interactions between bile salts or derivatives with ciprofloxacin and particularly gentamicin represent a promising strategy for the treatment of A. baumannii wound infections.

Interactions of bile salts with a dietary fibre, methylcellulose, and impact on lipolysis

Methylcellulose (MC) has a demonstrated capacity to reduce fat absorption, hypothetically through bile salt (BS) activity inhibition. We investigated MC cholesterol-lowering mechanism, and compared the influence of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ slightly by their architecture and exhibit contrasting functions during lipolysis.BS/MC bulk interactions were investigated by rheology, and BS behaviour at the MC/water interface studied with surface pressure and ellipsometry measurements. In vitro lipolysis studies were performed to evaluate the effect of BS on MC-stabilised emulsion droplets microstructure, with confocal microscopy, and free fatty acids release, with the pH-stat method.Our results demonstrate that BS structure dictates their interactions with MC, which, in turn, impact lipolysis. Compared to NaTC, NaTDC alters MC viscoelasticity more significantly, which may correlate with its weaker ability to promote lipolysis, and desorbs from the interface at lower concentrations, which may explain its higher propensity to destabilise emulsions.

Interaction of Bile Salts With Lipid Bilayers: An Atomistic Molecular Dynamics Study.

Bile salts (BS) are biosurfactants crucial for emulsification and intestinal absorption of cholesterol and other hydrophobic compounds such as vitamins and fatty acids. Interaction of BS with lipid bilayers is important for understanding their effects on membranes properties. The latter have relevance in passive diffusion processes through intestinal epithelium such as reabsorption of BS, as well as their degree of toxicity to intestinal flora and their potential applications in drug delivery. In this work, we used molecular dynamics simulations to address at the atomic scale the interactions of cholate, deoxycholate, and chenodeoxycholate, as well as their glycine conjugates with POPC bilayers. In this set of BS, variation of three structural aspects was addressed, namely conjugation with glycine, number and position of hydroxyl substituents, and ionization state. From atomistic simulations, the location and orientation of BS inside the bilayer, and their specific interactions with water and host lipid, such as hydrogen bonding and ion-pair formation, were studied in detail. Membrane properties were also investigated to obtain information on the degree of perturbation induced by the different BS. The results are described and related to a recent experimental study (Coreta-Gomes et al., 2015). Differences in macroscopic membrane partition thermodynamics and translocation kinetics are rationalized in terms of the distinct structures and atomic-scale behavior of the bile salt species. In particular, the faster translocation of cholate is explained by its higher degree of local membrane perturbation. On the other hand, the relatively high partition of the polar glycine conjugates is related to the longer and more flexible side chain, which allows simultaneous efficient solvation of the ionized carboxylate and deep insertion of the ring system.

Interaction of Bile Salts with Cetylpyridinium Chloride: Surface Tension and Viscosity Measurements

Background: Bile salts possess unique chemical structural characteristics and are very different from conventional surfactants. Due to the fascinating physiological functions, the bile salts have been widely studied by various physical methods. Last three decades are the witness about rapid studies on bile salts aggregation with surfactant but yet uncertain related to mixed micellar system. Objective: The primary objective of this study was to undertake systematic studies on the mixed systems comprising of cationic surfactant CPyCl + bile salts in water and NaCl solution by surface tension and viscosity method. Methods: Drop weight method (surface tension method) and viscometry methods are chosen to discuss the interaction between bile salts and surfactant mixed system. Results: Systematic studies on CPyCl + bile salts were carried out using Rubingh’s regular solution theory in presence/absence of NaCl. The CMC and viscosity data measurements were recorded. Molecular interaction parameters β was calculated to determine the depth of synergism between the micellar systems. Conclusions: Synergisms occur when cationic surfactant CPyCl and bile salts such as NaDC/NaC were mixed. NaCl has the ability to modify the structure of CPyCl and bile salts. Micelle size grows with increase in NaCl concentration. CMC of CPyCl decreases as the concentration of salts increases. Viscosity data reveals that size of CPyCl micelle increases with increasing NaCl concentration. Keywords: Bile salt, micellization, surfactant, CMC, hydrographic, aliphatic.

Bile salt–bile salt interaction in mixed monolayer and mixed micelle formation

Abstract Surface tension and steady-state fluorescence measurements have been done for mixtures of bile salts, namely sodium cholate (NaC) + sodium tourocholate (NaTC) and sodium cholate + sodium de-oxycholate (NaDC) at 298.15 K. From the experimental critical micelle concentration (cmc), the interaction parameter has been figured utilizing the regular solution theory proposed by Rubingh for mixed surfactant systems. The ideal cmc values and thermodynamic properties of micellization were evaluated. The Rosen model was used to calculate the various surface parameters. The interaction between NaC + NaDC surfactants was observed to be stronger than in NaC + NaTC. The stronger interaction of NaC + NaDC was also confirmed by fluorescence data. The steady-state fluorescence quenching method was applied to compute the micelle aggregation number, Stern-Volmer constant and micropolarity of single and mixed bile salt systems.

Interaction of a bile salt (sodium taurocholate) with cationic (ε-polylysine) and anionic (pectin) biopolymers under simulated gastrointestinal conditions

Dietary fibers are known to have beneficial effects on human health, which is partially attributed to their interactions with components in the gastrointestinal tract. In this study, the interaction of model bile salts with anionic (pectin) and cationic (polylysine) food-grade biopolymers, and their electrostatic complex, was examined. Isothermal titration calorimetry and titration measurements were used to characterize the nature of the interactions between the biopolymers and bile salts. Analysis of isothermal titration calorimetry data showed a marked difference for the taurocholate-pectin and taurocholate-ε-polylysine complexes, suggesting that sodium taurocholate binds strongly to ε-polylysine, presumably due to the attraction of oppositely electrical charges. While, the interaction between sodium taurocholate and pectin seems to be dominated by hydrophobic forces. On the other hand, the interaction of sodium taurocholate with a mixture of the two biopolymers showed a behavior that combined the characteristics of the individual systems. These results may have important implications for the design of functional foods to improve human health and wellness.

Binding orientation and interaction of bile salt in its ternary complex with pancreatic lipase-colipase system

The interfacial activity of pancreatic lipases (PL) depends on the presence of colipase and bile salt. The activity of PL is inhibited by micellar concentrations of bile salt which can be restored by the addition of colipase. Though the formation of 1:1:1 tertiary complex by lipase-colipase-bile salt micelle is well accepted, the residue-level interactions between lipase-colipase and bile salt are yet to be clearly understood. Molecular dynamic simulations of lipase-colipase complex, lipase and colipase were performed in the presence of a model bile salt, sodium taurocholate (NaTC), at its near-CMC and supra-micellar concentrations. From the interactions obtained from the molecular dynamic simulations, the ternary complex was modelled and compared with earlier reports. The analysis suggested that a micelle of NaTC consisting of nine monomers was formed at the concave groove between lipase and colipase chain and it mainly interacted with the fourth finger of colipase. This complex was mainly stabilized by van der Waals interactions. Interestingly, the C-terminal domain of lipase which holds the colipase did not show any significant role in formation or stabilization of NaTC micelle.

Mixed micelle formation of cationic gemini surfactant with anionic bile salt: a PAH solubilization study

Aqueous mixed micelle formation between cationic gemini surfactant (butanediyl-1,4-bis (N,N-alkyl ammonium) dibromide, m-4-m; or ethane-1,2-diyl (N,N-dimethyl-N-dodecyl-alkyl ammoniumacetoamide) dichloride, m-Eda-m, where m=12,14 and 16) and bile salt (sodium cholate, SC or sodium deoxycholate, SDC) has been investigated by conductivity measurements and the critical micelle concentration values are compared with individual gemini surfactant or bile salt. Surfactant–bile salt interactions (interaction parameter, βm) have been compared using theoretical models of Clint, Rubingh and Motomura. cmc values, with varying mole fractions of CG or bile salt, were used to obtain composition of binary mixture for PAH solubilization. Solubilization studies of polycyclic aromatic hydrocarbons PAHs, fluorene, anthracene and pyrene, have also been performed spectrophotometrically in aqueous cationic gemini (CG) with or without bile salt (SC or SDC). Individual bile salt nearly failed to solubilize any amount of PAHs. The solubilization potential has been discussed in the light of molar solubilization ratio (MSR) and compared with other similar CG-anionic surfactant systems. This is the first study in which oppositely charged CG-bile salt binary mixtures are used to enhance aqueous solubility of PAHs. The study may find potential use in biomedical applications.

Interaction of Bile Salts with β-Cyclodextrins Reveals Nonclassical Hydrophobic Effect and Enthalpy-Entropy Compensation.

Herein, we present an endeavor toward exploring the lacuna underlying the host:guest chemistry of inclusion complex formation between bile salt(s) and β-cyclodextrin(s) (βCDs). An extensive thermodynamic investigation based on isothermal titration calorimetry (ITC) demonstrates a dominant contribution from exothermic enthalpy change (ΔH < 0) accompanying the phenomenon of inclusion complex formation, along with a relatively smaller contribution to total free energy change from the entropic component. However, the negative heat capacity change (ΔCp < 0) displays the hallmark for a pivotal role of hydrophobic effect underlying the interaction. Contrary to the classical hydrophobic effect, such apparently paradoxical thermodynamic signature has been adequately described under the notion of "nonclassical hydrophobic effect". On the basis of our results, the displacement of disordered water from hydrophobic binding sites has been argued to mark the enthalpic signature and the key role of such interaction forces is further corroborated from enthalpy-entropy compensation behavior showing indication for almost complete compensation. To this end, we have quantified the interaction of two bile salt molecules (namely, sodium deoxycholate and sodium glycocholate) with a series of varying chemical substituents on the host counterpart, namely, βCD, (2-hydroxypropyl)-βCD, and methyl βCD.

Thermodynamics and Structural Evolution during a Reversible Vesicle-Micelle Transition of a Vitamin-Derived Bolaamphiphile Induced by Sodium Cholate.

Interaction of endogenous sodium cholate (SC) with dietary amphiphiles would induce structural evolution of the self-assembled aggregates, which inevitably affects the hydrolysis of fat in the gut. Current work mainly focused on the interaction of bile salts with classical double-layered phospholipid vesicles. In this paper, the thermodynamics and structural evolution during the interaction of SC with novel unilamellar vesicles formed from vitamin-derived zwitterionic bolaamphiphile (DDO) were characterized. It was revealed that an increased temperature and the presence of NaCl resulted in narrowed micelle-vesicle coexistence and enlarged the vesicle region. The coexistence of micelles and vesicles mainly came from the interaction of monomeric SC with DDO vesicles, whereas micellar SC contributed to the total solubilization of DDO vesicles. This research may enrich the thermodynamic mechanism behind the structure transition of the microaggregates formed by amphiphiles in the gut. It will also contribute to the design of food formulation and drug delivery system.

Mixed Micelle Formation between an Amino Acid-Based Anionic Gemini Surfactant and Bile Salts

The mixed micelle formation in basic aqueous solutions between an anionic gemini amino acid-based surfactant derived from cysteine (C8Cys)2 and the bile salts sodium cholate (NaC) and sodium deoxycholate (NaDC) has been studied by conductivity, and the results have been compared with the ones obtained for binary solutions of (C8Cys)2 with the conventional anionic surfactant sodium dodecyl sulfate (SDS). A nonideal mixing pattern was observed for the mixed systems, and a striking behavior was found for the gemini surfactant–bile salt mixtures, with gemini–bile salt interactions changing from synergistic to antagonistic with increasing gemini surfactant composition, whereas for the (C8Cys)2/SDS mixed system, synergism was attained over all the molar fraction range studied. Regular solution theory (RST) was used to analyze the gemini surfactant–anionic surfactant binary mixtures, and the interaction parameter (β) has been evaluated, as well as mixed micelle composition.

Alterations in nanoparticle protein corona by biological surfactants: Impact of bile salts on β-lactoglobulin-coated gold nanoparticles

The impact of biological surfactants (bile salts) on the protein (β-lactoglobulin) corona surrounding gold nanoparticles (200nm) was studied using a variety of analytical techniques at pH 7: dynamic light scattering (DLS); particle electrophoresis (ζ-potential); UV–visible (UV) spectroscopy; transmission electron microscopy (TEM); and surface-enhanced Raman scattering (SERS). The bile salts adsorbed to the protein-coated nanoparticle surfaces and altered their interfacial composition, charge, and structure. SERS spectra of protein-coated nanoparticles after bile salt addition contained bands from both protein and bile salts, indicating that the protein was not fully displaced by the bile salts. UV, DLS and TEM techniques also indicated that the protein coating was not fully displaced from the nanoparticle surfaces. The impact of bile salts could be described by an orogenic mechanism: mixed interfaces were formed that consisted of islands of aggregated proteins surrounded by a sea of bile salts. This knowledge is useful for understanding the interactions of bile salts with protein-coated colloidal particles, which may be important for controlling the fate of colloidal delivery systems in the human gastrointestinal tract, or the gastrointestinal fate of ingested inorganic nanoparticles.

Study on interaction of bile salts with curcumin and curcumin embedded in dipalmitoyl-sn-glycero-3-phosphocholine liposome

Curcumin, often used as a food spice, is a natural polyphenol that has various medicinal benefits such as anti-cancer, anti-amyloid, anti-oxidant, and anti-inflammatory properties, among others. The interaction between bile salts having physiological significance and curcumin suggests the aggregation of bile salts dramatically alters the absorption and fluorescence parameters of curcumin. The fluorescence emission maximum as well as the intensity can easily detect critical micellar concentration of sodium cholate and sodium deoxycholate respectively to be 16 and 6mM at room temperature. The mechanism of interaction of curcumin with bile salts has been presented at low, intermediate and high bile salt concentrations and depends on temperature. In the presence of bile salts the DPPH scavenging activity was preserved, though less than in the presence of curcumin alone. The effect of submicellar concentration, 5–50μM, of bile salt with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes in solid gel and liquid crystalline phases has been investigated using curcumin as an embedded probe in the membrane. The curcumin based fluorescence probing method indicates even at very low concentration, ∼5μM, incorporation of monomeric bile salt molecules disorders the membrane properties. Expulsion of curcumin from the membrane in the presence of bile salt is ruled out, suggesting wetting of membrane. Alteration of membrane fluidity by bile salts is found to have an opposing effect in the liquid crystalline phase compared to in the solid gel phase, and is sensitive to the nature of bile salt. The permeability in the liquid crystalline phase decreases in the presence of bile salt. The phase transition temperature of the membrane is influenced by bile salt.

Bile salt- and lysophosphatidylcholine-induced membrane damage in human erythrocytes.

The interaction of bile salts and lysophosphatidylcholine (LPC) with membranes has implications both in understanding the aetiology of a number of gastrointestinal disorders, including gastritis, gastric ulcers and colonic cancer, and in enhancing drug absorption by various epithelia. The membrane toxicity of nine bile salts (the sodium (S) salts of chenodeoxycholate (CDC), deoxycholate (DC) and cholate (C) and their glycine (G) and taurine (T) conjugates) and LPC was determined using erythrocyte haemolysis as a model parameter. Washed human erythrocytes were incubated for 15-60 min at 20 degrees C with media buffered at pH 8, 7 and 6. Bile salt toxicity was shown to be a function of type, concentration, pH and contact time with the membrane. At pH 7 toxicity decreased in the order LPC greater than unconjugated dihydroxy salts (SDC and SCDC) greater than conjugated deoxycholates (SGDC and STDC) greater than conjugated chenodeoxycholates (SGCDC and STCDC) greater than unconjugated trihydroxy salt (SC) greater than conjugated trihydroxy salts (SGC and STC). Incubation with equimolar combinations of bile salts (SDC+SCDC; STCDC+SGDC; SDC+STDC) indicated that the resultant damage was an additive function of the damage induced by the individual bile salts.

Proceedings: Micellar interactions of bile salts with alkytrimethylammonimum bromides.

Proceedings: Micellar interactions of bile salts with alkytrimethylammonimum bromides.

NMR Characterization of the Interaction of the Salmonella Type III Secretion System Protein SipD and Bile Salts,

Salmonella and Shigella bacteria require the type III secretion system (T3SS) to inject virulence proteins into their hosts and initiate infections. The tip proteins SipD and IpaD are critical components of the Salmonella and Shigella T3SS, respectively. Recently, SipD and IpaD have been shown to interact with bile salts, which are enriched in the intestines, and are hypothesized to act as environmental sensors for these enteric pathogens. Bile salts activate the Shigella T3SS but repress the Salmonella T3SS, and the mechanism of this differing response to bile salts is poorly understood. Further, how SipD binds to bile salts is currently unknown. Computer modeling predicted that IpaD binds the bile salt deoxycholate in a cleft formed by the N-terminal domain and the long central coiled coil of IpaD. Here, we used NMR methods to determine which SipD residues are affected by the interaction with the bile salts deoxycholate, chenodeoxycholate, and taurodeoxcholate. The bile salts perturbed nearly the same set of SipD residues; however, the largest chemical shift perturbations occurred away from what was predicted for the bile salt binding site in IpaD. Our NMR results indicate that that bile salt interaction of SipD will be different from what was predicted for IpaD, suggesting a possible mechanism for the differing response of Salmonella and Shigella to bile salts.