Synthesis of Nontoxic Fluorous Sphingolipids as Molecular Probes of Exogenous Metabolic Studies for Rapid Enrichment by Fluorous Solid Phase Extraction

Stereochemistry of Sphingolipids in Ganglioside GM3 Enhances Recovery of Nervous Functionality

GM3 is a simple monosialylated ganglioside (NeuAcα(2-3)Galβ(1-4)Glcβ1-1'-ceramide). Its aberrant expression in adipocytes is involved in a variety of physiological and pathological processes in diabetes mellitus and obesity. GM3 is exposed on the outer surface of cell membranes and is strongly associated with type 2 diabetes and insulin resistance. Exogenously added GM3 promotes neurite outgrowth in a variety of different neuroblastoma cell lines. Neurite outgrowth is a key process in the development of functional neuronal circuits and neuro-regeneration following nerve injury. Therefore, regulating GM3 levels in nerve tissues might be a potential treatment method for these disorders. Here, we demonstrate the comprehensive synthesis of stereoisomeric GM3s and compare their physicochemical properties with those of natural GM3 and diastereomers of sphingolipids in GM3 to examine the enhancement of biological activity. l-erythro-GM3 was confirmed to increase neurite outgrowth, providing valuable insights for potential neuro-regenerative treatments.

Stereochemistry-activity relationship of ceramide-induced exosome production to clear amyloid-β in Alzheimer's disease

Stereochemistry has a substantial impact on the biological activity of various drugs. We investigated the role of stereochemistry of ceramides in inducing the production of exosomes, a type of extracellular vesicle, from neuronal cells, with a potential benefit in improving the clearance of amyloid-β (Aβ), a causal agent of Alzheimer's disease. A stereochemical library of diverse ceramides with different tail lengths was synthesized with the purpose of varying stereochemistry (D-erythro: DE, D-threo: DT, L-erythro: LE, L-threo: LT) and hydrophobic tail length (C6, C16, C18, C24). The exosome levels were quantified using TIM4-based exosome enzyme-linked immunosorbent assay after concentrating the conditioned medium using centrifugal filter devices. The results revealed a pivotal role of stereochemistry in determining the biological activity of ceramide stereoisomers, with the superiority of those based on DE and DT stereochemistry with C16 and C18 tails, which demonstrated significantly higher exosome production, without a significant change in the particle size of the released exosomes. In transwell experiments with Aβ-expressed neuronal and microglial cells, DE- and DT-ceramides with C16 and C18 tails significantly decreased extracellular Aβ levels. The results reported here are promising in the design of non-classic therapies for the treatment of Alzheimer's disease.

Deciphering the Mechanistic Basis for Perfluoroalkyl-Protein Interactions

Although rarely used in nature, fluorine has emerged as an important elemental ingredient in the design of proteins with altered folding, stability, oligomerization propensities, and bioactivity. Adding to the molecular modification toolbox, here we report the ability of privileged perfluorinated amphiphiles to noncovalently decorate proteins to alter their conformational plasticity and potentiate their dispersion into fluorous phases. Employing a complementary suite of biophysical, in-silico and in-vitro approaches, we establish structure-activity relationships defining these phenomena and investigate their impact on protein structural dynamics and intracellular trafficking. Notably, we show that the lead compound, perfluorononanoic acid, is 106 times more potent in inducing non-native protein secondary structure in select proteins than is the well-known helix inducer trifluoroethanol, and also significantly enhances the cellular uptake of complexed proteins. These findings could advance the rational design of fluorinated proteins, inform on potential modes of toxicity for perfluoroalkyl substances, and guide the development of fluorine-modified biologics with desirable functional properties for drug discovery and delivery applications.

Structural insights into the substrate recognition of serine palmitoyltransferase from Sphingobacterium multivorum

Serine palmitoyltransferase (SPT) is a key enzyme of sphingolipid biosynthesis, which catalyzes the pyridoxal-5'-phosphate-dependent decarboxylative condensation reaction of L-serine (L-Ser) and palmitoyl-CoA (PalCoA) to form 3-ketodihydrosphingosine called long chain base (LCB). SPT is also able to metabolize L-alanine (L-Ala) and glycine (Gly), albeit with much lower efficiency. Human SPT is a membrane-bound large protein complex containing SPTLC1/SPTLC2 heterodimer as the core subunits, and it is known that mutations of the SPTLC1/SPTLC2 genes increase the formation of deoxy-type of LCBs derived from L-Ala and Gly to cause some neurodegenerative diseases. In order to study the substrate recognition of SPT, we examined the reactivity of Sphingobacterium multivorum SPT on various amino acids in the presence of PalCoA. The S. multivorum SPT could convert not only L-Ala and Gly but also L-homoserine, in addition to L-Ser, into the corresponding LCBs. Furthermore, we obtained high-quality crystals of the ligand-free form and the binary complexes with a series of amino acids, including a nonproductive amino acid, L-threonine, and determined the structures at 1.40-1.55 Å resolutions. The S. multivorum SPT accommodated various amino acid substrates through subtle rearrangements of the active-site amino acid residues and water molecules. It was also suggested that non-active-site residues mutated in the human SPT genes might indirectly influence the substrate specificity by affecting the hydrogen-bonding networks involving the bound substrate, water molecules, and amino acid residues in the active site of this enzyme. Collectively, our results highlight SPT structural features affecting substrate specificity for this stage of sphingolipid biosynthesis.

Penta-deuterium-labeled 4E, 8Z-sphingadienine for rapid analysis in sphingolipidomics study

The use of deuterium-incorporated bioactive compounds is an efficient method for tracing their metabolic fate and for quantitative analysis by mass spectrometry without complicated HPLC separation even if their amounts are extremely small. Plant sphingolipids and their metabolites, which have C4, 8-olefins on a common backbone as a sphingoid base, show unique and fascinating bioactivities compared to those of sphingolipids in mammals. However, the functional and metabolic mechanisms of exogenous plant sphingolipids have not been elucidated due to the difficulty in distinguishing exogenous sphingolipids from endogenous sphingolipids having the same polarity and same molecular weight by mass spectrometric analysis. Their roles might be elucidated by the use of deuterated probes with original biological and physicochemical properties. In this study, we designed (2S,3R,4E,8Z)-2-aminooctadeca-4,8-diene-17,17,18,18,18-d₅-1,3-diol (penta-deuterium-labeled 4E, 8Z-sphingadienine) as a tracer for exogenous metabolic studies. In addition, the sphingadienine was confirmed to be metabolized in HEK293 cells and showed distinct peaks in mass spectrometric analysis.

Evaluation of chiral N,N-dimethyl-sphingosine for the interaction between nerve growth factor and tropomyosin receptor kinase A

Neuropathic pain is an unbearable condition caused by nervous system damage. As distinct acute pain, neuropathic pain is chronic, and it severely influences quality of life. N,N-Dimethyl-d-erythro-sphingosine (DMS), a neuropathic pain inducer, is metabolited de novo from sphingosine. In a recent study, metabolomics showed an increased concentration level of DMS in the spinal cord in mice with neuropathic pain. Nerve growth factor (NGF) is one of the peripheral nervous system targeted pain factors that interact with tropomyosin receptor kinase A (trkA). On the basis of this information, we were interested in the possibility that DMS may induce neuropathic pain-like behavior through an increase of NGF activity. In this study, we showed that DMS can enhance the binding of NGF to trkA, followed by neurite outgrowth of epidermal nerve fibers and phosphorylation of trkA. In addition, a stereoisomer, N,N-dimethyl-l-erythro-sphingosine, did not any show such biological activities. The results suggest that DMS can enhance the binding of NGF to trkA and that its stereochemistry is an essential factor for exhibiting its activity.

Perfluorinated Probes for Noncovalent Protein Recognition and Isolation

Perfluorinated organic compounds (PFCs) are nontoxic, biocompatible, bioavailable, and bioorthogonal species which possess the unique ability to segregate away from both polar and nonpolar solvents producing a compact fluorophilic phase. Traditional techniques of fluorous chemical proteomics are generally applied to enrich biological samples in target protein(s) exploiting this property of PFCs to build fluorinated probes able to covalently bind to protein ensembles and being selectively extracted by fluorophilic solvents. Aiming at building a strategy able to avoid irreversible modification of the analyzed biosystem, a novel fully noncovalent probe is presented as an enabling tool for the recognition and isolation of biological protein(s). In our strategy, both the fluorophilic extraction and the biorecognition of a selected protein successfully occur via the establishment of reversible but selective interactions.