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Abstract Metabotropic glutamate receptor 2 (mGluR2), a subclass C member of the G protein-coupled receptor (GPCR) superfamily, is essential for regulating neurotransmitter signaling and facilitating synaptic adaptability in the central nervous system. This receptor, like other GPCRs, is highly sensitive to its surrounding lipid environment, where specific lipid compositions can influence its stability, conformational dynamics, and function. In particular, cholesteryl hemisuccinate (CHS) plays a critical role in stabilizing mGluR2 and modulating its structural states within cellular membranes and micellar environments. However, the molecular basis for this lipid-mediated modulation remains largely unexplored. To investigate the effects of CHS and lipid composition on mGluR2, we employed all-atom molecular dynamics simulations of mGluR2 embedded in both detergent micelles (BLMNG and CHS) and a POPC lipid bilayer containing 0%, 10%, and 25% CHS. These simulations were conducted for both active and inactive states of the receptor. Our findings reveal that CHS concentration modulates mGluR2’s structural stability and conformational behavior, with a marked impact observed within transmembrane helices TM1, TM2, and TM3, which constitute the core of the receptor’s transmembrane domain. In micelle environments, mGluR2 displayed unique conformational dynamics influenced by CHS, underscoring the receptor’s sensitivity to its lipid surroundings. Notably, a CHS concentration of 10% elicited more pronounced conformational changes than either cholesterol-depleted (0%) or cholesterol-enriched (25%) systems, indicating an optimal CHS range for maintaining structural stability. Our study provides atomistic insights into how lipid composition and CHS concentration impact mGluR2’s conformational landscape in distinct micelle and bilayer environments. These findings advance our understanding of lipid-mediated modulation in GPCR function, highlighting potential avenues for receptor-targeted drug design, particularly in cases where lipid interactions play a significant role in therapeutic efficacy. 

Archaeal group II chaperonins, also known as heat shock proteins (HSPs), are abundantly expressed in Sulfolobales. HSPα and HSPβ gene expression is upregulated during thermal shock. HSPs form large 18-mer complexes that assist in folding nascent proteins and protecting resident proteins during thermal stress. Engineered HSPs have been designed for industrial applications. Since temperature flux in the geothermal habitats of Sulfolobales impacts intracellular temperature, it follows that HSPs have developed thermotolerance. However, despite the low pH (i.e., pH < 4) typical for these habitats, intracellular pH in Sulfolobales is maintained at ~6.5. Therefore, it is not presumed that HSPs have evolved acid-tolerance. To test tolerance to low pH, HSPs were studied at various pH and temperature values. Both circular dichroism and intrinsic fluorescence indicate that HSPα and HSPβ retain structural integrity at neutral pH over a wide range of temperatures. Structural integrity is compromised for all HSPs at ultra-low pH (e.g., pH 2). Secondary structures in HSPs are resilient under mildly acidic conditions (pH 4) but Anilino naphthalene 8-sulfonate binding shows shifts in tertiary structure at lower pH. Trypsin digestion shows that the HSPβ-coh backbone is the most flexible and HSPβ is the most resilient. Overall, results suggest that HSPα and HSPβ exhibit greater thermostability than HSPβ-coh and that there are limits to HSP acid-tolerance. Molecular dynamics (MD) simulations complement the wet lab data. Specifically, MD suggests that the HSPβ secondary structure is the most stable. Also, despite similarities in pH- and temperature-dependent behavior, there are clear differences in how each HSP subtype is perturbed. 

Abstract Sav1866, a bacterial ATP-binding cassette (ABC) exporter, plays a crucial role in cellular processes by facilitating the efflux of a diverse range of substrates, including drugs, chemotherapeutic agents, peptides, and lipids. This efflux activity significantly impacts the effectiveness of various therapies against bacterial infections. In our recent investigation, we focused on understanding the conformational dynamics of Sav1866 within different lipid environments. Specifically, we explored its behavior in environments composed of DMPC and POPE lipids, which exhibit crucial distinctions not only in their headgroup polarity but also in the length and saturation of their hydrophobic tails. Our extensive set of equilibrium microsecond-level all-atom molecular dynamics (MD) simulations revealed significant distinctions in transporter behavior influenced by these lipid compositions. We observed a rapid transition to an occluded-inward-facing (IF-occ) conformation in POPE environments, contrasting with a channel-like behavior in DMPC environments, deviating from the expected alternating access mechanism (AAM). These findings underscore the significant impact of lipid compositions on ABC transporter function, offering new perspectives on membrane transport mechanisms. 

Abstract Metabotropic glutamate receptors (mGluRs) are class C G protein-coupled receptors that function as obligate dimers in regulating neurotransmission and synaptic plasticity in the central nervous system. The mGluR1 subtype has been shown to be modulated by the membrane lipid environment, particularly cholesterol, though the molecular mechanisms remain elusive. In this study, we employed all-atom molecular dynamics simulations to investigate the effects of cholesterol on the conformational dynamics of the mGluR1 seven-transmembrane (7TM) domain in an inactive state model. Simulations were performed with three different cholesterol concentrations (0%, 10%, and 25%) in a palmitoyl-oleoyl phosphatidylcholine (POPC) lipid bilayer system. Our results demonstrate that cholesterol induces conformational changes in the mGluR1 dimer more significantly than in the individual protomers. Notably, cholesterol modulates the dynamics and conformations of the TM1 and TM2 helices at the dimer interface. Interestingly, an intermediate cholesterol concentration of 10% elicits more pronounced conformational changes compared to both cholesterol-depleted (0%) and cholesterol-enriched (25%) systems. Specific electrostatic interaction unique to the 10% cholesterol system further corroborate these conformational differences. Given the high sequence conservation of the 7TM domains across mGluR subtypes, the cholesterol-dependent effects observed in mGluR1 are likely applicable to other members of this receptor family. Our findings provide atomistic insights into how cholesterol modulates the conformational landscape of mGluRs, which could impact their function and signaling mechanisms.