Integrity of the Actin Cytoskeleton of Host Macrophages is Necessary for Mycobacterial Entry.

Macrophages are the primary hosts for Mycobacterium tuberculosis (M. tb), an intracellular pathogen, and the causative organism of tuberculosis (TB) in humans. While M.

A molecular sensor for cholesterol in the human serotonin receptor.

The function of several G protein-coupled receptors (GPCRs) exhibits cholesterol sensitivity. Cholesterol sensitivity of GPCRs could be attributed to specific sequence and structural features, such as the cholesterol recognition/interaction amino acid consensus (CRAC) motif, that facilitate their cholesterol-receptor interaction. In this work, we explored the molecular basis of cholesterol sensitivity exhibited by the serotonin receptor, the most studied GPCR in the context of cholesterol sensitivity, by generating mutants of key residues in CRAC motifs in transmembrane helix 2 (TM2) and TM5 of the receptor.

Structural Stringency and Optimal Nature of Cholesterol Requirement in the Function of the Serotonin Receptor.

The role of membrane cholesterol in modulating G protein-coupled receptor (GPCR) structure and function has emerged as a powerful theme in contemporary biology. In this paper, we report the subtlety and stringency involved in the interaction of sterols with the serotonin receptor. For this, we utilized two immediate biosynthetic precursors of cholesterol, 7-dehydrocholesterol (7-DHC) and desmosterol, which differ with cholesterol merely in a double bond in their chemical structures in a position-dependent manner.

Exploring Endocytosis and Intracellular Trafficking of the Human Serotonin Receptor.

G protein-coupled receptors (GPCRs) represent the largest class of receptors involved in signal transduction across cell membranes and are major drug targets in all clinical areas. Endocytosis of GPCRs offers a regulatory mechanism for sustaining their signaling within a stringent spatiotemporal regime. In this work, we explored agonist-induced endocytosis of the human serotonin receptor stably expressed in HEK-293 cells and the cellular machinery involved in receptor internalization and intracellular trafficking.

A Critical Analysis of Molecular Mechanisms Underlying Membrane Cholesterol Sensitivity of GPCRs.

G protein-coupled receptors (GPCRs) are the largest and a diverse family of proteins involved in signal transduction across biological membranes. GPCRs mediate a wide range of physiological processes and have emerged as major targets for the development of novel drug candidates in all clinical areas. Since GPCRs are integral membrane proteins, regulation of their organization, dynamics, and function by membrane lipids, in particular membrane cholesterol, has emerged as an exciting area of research.

Identification of Sphingolipid-binding Motif in G Protein-coupled Receptors.

Sphingolipids correspond to a major class of lipids which serve as indispensable structural components of membranes and play an important role in various cellular functions. They constitute ~10-20% of total membrane lipids and are known to form segregated domains in biological membranes. Sphingolipids have been shown to play a vital role in the function of various G protein-coupled receptors (GPCRs).

Macrophage sphingolipids are essential for the entry of mycobacteria.

Mycobacteria are intracellular pathogens that can invade and survive within host macrophages. Mycobacterial infections remain a major cause of mortality and morbidity worldwide, with serious concerns of emergence of multi and extensively drug-resistant tuberculosis. While significant advances have been made in identifying mycobacterial virulence determinants, the detailed molecular mechanism of internalization of mycobacteria into host cells remains poorly understood.

Exploring oligomeric state of the serotonin receptor utilizing photobleaching image correlation spectroscopy: implications for receptor function.

The oligomerization of G protein-coupled receptors (GPCRs) represents an important process in GPCR function and drug discovery. We have addressed cholesterol-dependent oligomerization state of the serotonin receptor, a representative GPCR and an important drug target, utilizing photobleaching image correlation spectroscopy (pbICS). pbICS allows determination of oligomeric state of membrane receptors since change in cluster density upon photobleaching is dependent on the oligomeric state.

Structural Stringency of Cholesterol for Membrane Protein Function Utilizing Stereoisomers as Novel Tools: A Review.

Cholesterol is an important lipid in the context of membrane protein function. The function of a number of membrane proteins, including G protein-coupled receptors (GPCRs) and ion channels, has been shown to be dependent on membrane cholesterol. However, the molecular mechanism underlying such regulation is still being explored.

Membrane cholesterol oxidation in live cells enhances the function of serotonin receptors.

The serotonin (5-HT) receptor is an important neurotransmitter receptor that belongs to the G protein-coupled receptor (GPCR) family. It is implicated in a variety of cognitive and behavioral functions and serves as an important drug target for neuropsychiatric disorders such as anxiety and depression. Previous work from our laboratory has demonstrated that membrane cholesterol plays an important role in the function of the serotonin receptor.

Sphingolipids modulate the function of human serotonin receptors: Insights from sphingolipid-deficient cells.

Sphingolipids are essential components of eukaryotic cell membranes and are known to modulate a variety of cellular functions. It is becoming increasingly clear that membrane lipids play a crucial role in modulating the function of integral membrane proteins such as G protein-coupled receptors (GPCRs). In this work, we utilized LY-B cells, that are sphingolipid-auxotrophic mutants defective in sphingolipid biosynthesis, to monitor the role of cellular sphingolipids in the function of an important neurotransmitter receptor, the serotonin receptor.

The ganglioside GM1 interacts with the serotonin receptor via the sphingolipid binding domain.

Glycosphingolipids are minor yet essential components of eukaryotic cell membranes and are involved in a variety of cellular processes. Although glycosphingolipids such as GM1 have been previously reported to influence the function of G protein-coupled receptors (GPCRs), the molecular mechanism remains elusive. In this paper, we have explored the interaction of GM1 with the serotonin receptor, an important neurotransmitter receptor that belongs to the GPCR family.

Statin-induced chronic cholesterol depletion inhibits Leishmania donovani infection: Relevance of optimum host membrane cholesterol.

Leishmania are obligate intracellular protozoan parasites that invade and survive within host macrophages leading to leishmaniasis, a major cause of mortality and morbidity worldwide, particularly among economically weaker sections in tropical and subtropical regions. Visceral leishmaniasis is a potent disease caused by Leishmania donovani. The detailed mechanism of internalization of Leishmania is poorly understood.

Cholesterol modulates bitter taste receptor function.

Bitter taste perception in humans is believed to act as a defense mechanism against ingestion of potential toxic substances. Bitter taste is perceived by 25 distinct bitter taste receptors (T2Rs) which belong to the family of G protein-coupled receptors (GPCRs). In the overall context of the role of membrane lipids in GPCR function, we show here that T2R4, a representative member of the bitter taste receptor family, displays cholesterol sensitivity in its signaling function.

The membrane as the gatekeeper of infection: Cholesterol in host-pathogen interaction.

The cellular plasma membrane serves as a portal for the entry of intracellular pathogens. An essential step for an intracellular pathogen to gain entry into a host cell therefore is to be able to cross the cell membrane. In this review, we highlight the role of host membrane cholesterol in regulating the entry of intracellular pathogens using insights obtained from work on the interaction of Leishmania and Mycobacterium with host cells.

Dissecting the membrane cholesterol requirement for mycobacterial entry into host cells.

Mycobacteria are intracellular pathogens that can invade and survive within host macrophages, and are a major cause of mortality and morbidity worldwide. The molecular mechanism involved in the internalization of mycobacteria is poorly understood. In this work, we have explored the role of host membrane cholesterol in the entry of the avirulent surrogate mycobacterial strain Mycobacterium smegmatis into THP-1 macrophages.

Solubilization of G protein-coupled receptors: a convenient strategy to explore lipid-receptor interaction.

G protein-coupled receptors (GPCRs) are the largest class of molecules involved in signal transduction across cell membranes and are major drug targets. Since GPCRs are integral membrane proteins, their structure and function are modulated by membrane lipids. In particular, membrane cholesterol is an important lipid in the context of GPCR function.

Integrity of the actin cytoskeleton of host macrophages is essential for Leishmania donovani infection.

Visceral leishmaniasis is a vector-borne disease caused by an obligate intracellular protozoan parasite Leishmania donovani. The molecular mechanism involved in internalization of Leishmania is poorly understood. The entry of Leishmania involves interaction with the plasma membrane of host cells.

Stereospecific requirement of cholesterol in the function of the serotonin1A receptor.

The serotonin1A receptor is an important member of the G protein-coupled receptor (GPCR) family. It is involved in the generation and modulation of a variety of cognitive and behavioral functions and serves as a drug target. Previous work from our laboratory has established the sensitivity of the function of the serotonin1A receptor to membrane cholesterol.

Membrane lipids in the function of serotonin and adrenergic receptors.

G-protein coupled receptors (GPCRs) are the largest class of molecules involved in signal transduction across membranes, and represent major targets in the development of novel drug candidates in all clinical areas. Since GPCRs are integral membrane proteins, interaction of membrane lipids such as cholesterol and sphingolipids with GPCRs constitutes an emerging area of research in contemporary biology. Cholesterol and sphingolipids represent important lipid components of eukaryotic membranes and play a crucial role in a variety of cellular functions.

A novel mechanism for an old drug: amphotericin B in the treatment of visceral leishmaniasis.

Visceral leishmaniasis (VL) is caused by various species of the genus Leishmania. Internalization of Leishmania into host cells is facilitated by a large number of receptors, and therefore no panacea is available for the treatment of leishmaniasis. We previously demonstrated the requirement of host membrane cholesterol in the entry of Leishmania into macrophages by cholesterol depletion using methyl-β-cyclodextrin (MβCD).

Targeted liposomes to deliver DNA to cells expressing 5-HT receptors.

Cell targeted delivery of drugs, including nucleic acids, is known to enhance the therapeutic potential of free drugs. We used serotonin (5-HT) as the targeting ligand to deliver plasmid DNA to cells specifically expressing 5-HT receptor. Our liposomal formulation includes the 5-HT conjugated targeting lipid, a cationic lipid and cholesterol.

Desmosterol replaces cholesterol for ligand binding function of the serotonin(1A) receptor in solubilized hippocampal membranes: support for nonannular binding sites for cholesterol?

The serotonin(1A) receptor is an important member of the G-protein coupled receptor family, and is involved in the generation and modulation of a variety of cognitive and behavioral functions. Solubilization of the hippocampal serotonin(1A) receptor by CHAPS is accompanied by loss of cholesterol that results in a reduction in specific agonist binding activity. Replenishment of cholesterol to solubilized membranes restores membrane cholesterol content and significantly recovers specific agonist binding.