Preparation of Nitrogen Analogues of Ceramide and Studies of Their Aggregation in Sphingomyelin Bilayers

Abstract

Ceramides can regulate biological processes probably through the formation of laterally segregated and highly packed ceramide-rich domains in lipid bilayers. In the course of preparation of its analogues, we found that a hydrogen-bond-competent functional group in the C1 position is necessary to form ceramide-rich domains in lipid bilayers [ Matsufuji Matsufuji Langmuir2018]. Hence, in the present study, we newly synthesized three ceramide analogues: CerN3, CerNH2, and CerNHAc, in which the 1-OH group of ceramide is substituted with a nitrogen functionality. CerNH2 and CerNHAc are capable of forming hydrogen bonds in their headgroups, whereas CerN3 is not. Fluorescent microscopy observation and differential scanning calorimetry analysis disclosed that these ceramide analogues formed ceramide-rich phases in sphingomyelin bilayers, although their thermal stability was slightly inferior to that of normal ceramides. Moreover, wide-angle X-ray diffraction analysis showed that the chain packing structure of ceramide-rich phases of CerNHAc and CerN3 was similar to that of normal ceramide, while the CerNH2-rich phase showed a slightly looser chain packing due to the formation of CerNH3 +. Although the domain formation of CerN3 was unexpected because of the lack of hydrogen-bond capability in the headgroup, it may become a promising tool for investigating the mechanistic link between the ceramide-rich phase and the ceramide-related biological functions owing to its Raman activity and applicability to click chemistry.

Inimitable Impacts of Ceramides on Lipid Rafts Formed in Artificial and Natural Cell Membranes

“…While ceramide is central to signal transduction regulation, the biological functions of natural ceramides are poorly accessible because ceramide is readily transformed into more complex sphingolipids, such as SM and glycosphingolipids, via the modification of its 1-OH group [ 64 , 92 ]. To avoid this biosynthetic conversion, our group developed oxidised and nitrogen analogues of ceramides, in which the primary alcohol moiety was derivatised to -COOH, -COOMe, -NH 2 , -NHAc, and -N 3 groups ( Figure 6 ) [ 102 , 103 ]. In addition, we observed their capability of the domain formation in SM and POPC bilayers.…”

“… Chemical structures of 1-OH group substituted ceramide analogues developed in [ 102 , 103 ]. Protective groups are indicated by red colour.…”