pH Dependence of Sphingosine Aggregation

• Published in: Biophysical journal Vol. 96; no. 7; pp. 2727 - 2733
• Main Authors: Sasaki, Hirotaka, Arai, Hiromi, Cocco, Melanie J., White, Stephen H.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 08.04.2009; Biophysical Society; The Biophysical Society
• Subjects: Apoptosis; Cell growth; Hydrogen Bonding; Hydrogen-Ion Concentration; Light; Lysophospholipids - metabolism; Magnetic Resonance Spectroscopy; Membrane; Micelles; NMR; Nuclear magnetic resonance; Scattering; Scattering, Radiation; Signal transduction; Spectrum analysis; Sphingosine - analogs & derivatives; Sphingosine - chemistry; Sphingosine - metabolism; Titrimetry
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2008.12.3926

Sphingosine and sphingosine 1-phosphate (S1P) are sphingolipid metabolites that act as signaling messengers to activate or inhibit multiple downstream targets to regulate cell growth, differentiation, and apoptosis. The amphiphilic nature of these compounds leads to aggregation above their critical micelle concentrations (CMCs), which may be important for understanding lysosomal glycosphingolipid storage disorders. We investigated the aggregation of sphingosine and S1P over a comprehensive, physiologically relevant range of pH values, ionic strengths, and lipid concentrations by means of dynamic light scattering, titration, and NMR spectroscopy. The results resolve discrepancies in literature reports of CMC and pK a values. At physiological pH, the nominal CMCs of sphingosine and S1P are 0.99 ± 0.12 μM (pH 7.4) and 14.35 ± 0.08 μM (pH 7.2), respectively. We find that pH strongly affects the aggregation behavior of sphingosine by changing the ionic and hydrogen-bonding states; the nominal critical aggregation concentrations of protonated and deprotonated sphingosine are 1.71 ± 0.24 μM and 0.70 ± 0.02 μM, respectively. NMR measurements revealed that the NH 3 +–NH 2 transition of sphingosine occurs at pH 6.6, and that there is a structural shift in sphingosine aggregates caused by a transition in the predominant hydrogen-bonding network from intramolecular to intermolecular that occurs between pH 6.7 and 9.9.