In enzymology, a sphingomyelin synthase (EC 2.7.8.27) is an enzyme that catalyzes the chemical reaction
| SMSr-ceramide | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 The cryo-EM structure of human sphingomyelin synthase-related protein in complex with ceramide. PDB 8IJQ | |||||||||
| Identifiers | |||||||||
| EC no. | 2.7.8.27 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / QuickGO | ||||||||
| |||||||||
- a ceramide + a phosphatidylcholine a sphingomyelin + a 1,2-diacyl-sn-glycerol
or the reaction using phosphatidylethanolamine instead of phosphatidylcholine to generate ceramide phosphoethanolamine (CPE), a sphingomyelin analog rich in invertebrates, such as insects.
Thus, the two substrates of this enzyme are ceramide and phosphatidylcholine, whereas its two products are sphingomyelin and 1,2-diacyl-sn-glycerol.
This enzyme belongs to the family of transferases, specifically those transferring non-standard substituted phosphate groups. The systematic name of this enzyme class is ceramide:phosphatidylcholine cholinephosphotransferase. Other names in common use include SM synthase, SMS1, and SMS2. SM synthase family also includes the enzyme catalyzing CPE synthesis, named SMSr (SMS-related).
Structure of SM synthases
editThe high sequence identities shared among the three members of the Sphingomyelin Synthase (SMS) family have intrigued researchers for years. Recent cryo-electron microscopic studies have unveiled a fascinating hexameric organization specifically for SMSr,[1] while biochemical investigations have highlighted the formation of stable dimers by SMS1 and SMS2.[2] Within this hexameric structure, each monomeric unit of SMSr functions as an independent catalytic entity, characterized by six transmembrane helices.
The structural analysis has revealed the presence of a sizable chamber within the helical bundle of SMSr. This chamber serves as the site for catalytic activity, with researchers pinpointing a catalytic pentad, denoted as E-H/D-H-D, strategically positioned at the interface between the lipophilic and hydrophilic segments of the reaction chamber. Furthermore, the elucidation of SMSr's catalytic mechanism has uncovered an intricate two-step synthesis process for SM synthesis. Initially, phosphoethanolamine (or phosphatidylcholine in case of SMS1/2) is hydrolyzed from phosphatidylethanolamine (PE-PLC hydrolysis), followed by the subsequent transfer of the phosphoethanolamine moiety to ceramide.
References
edit- ^ Hu K, Zhang Q, Chen Y, Yang J, Xia Y, Rao B, et al. (2024). "Cryo-EM structure of human sphingomyelin synthase and its mechanistic implications for sphingomyelin synthesis". Nat Struct Mol Biol: 1–12. doi:10.1038/s41594-024-01237-2.
- ^ Hayashi Y, Nemoto-Sasaki Y, Matsumoto N, Tanikawa T, Oka S, Tanaka Y, et al. (January 2017). "Carboxyl-terminal Tail-mediated Homodimerizations of Sphingomyelin Synthases Are Responsible for Efficient Export from the Endoplasmic Reticulum". Journal of Biological Chemistry. 292 (3): 1122–1141. doi:10.1074/jbc.M116.746602. PMC 5247646. PMID 27927984.
- Ullman MD, Radin NS (1974). "The enzymatic formation of sphingomyelin from ceramide and lecithin in mouse liver". J. Biol. Chem. 249 (5): 1506–12. doi:10.1016/S0021-9258(19)42911-6. PMID 4817756.
- Voelker DR, Kennedy EP (1982). "Cellular and enzymic synthesis of sphingomyelin". Biochemistry. 21 (11): 2753–9. doi:10.1021/bi00540a027. PMID 7093220.
- Huitema K, van den Dikkenberg J, Brouwers JF, Holthuis JC (2004). "Identification of a family of animal sphingomyelin synthases". EMBO J. 23 (1): 33–44. doi:10.1038/sj.emboj.7600034. PMC 1271672. PMID 14685263.
- Tafesse FG, Ternes P, Holthuis JC (2006). "The multigenic sphingomyelin synthase family". J. Biol. Chem. 281 (40): 29421–5. doi:10.1074/jbc.R600021200. PMID 16905542.
- Yamaoka S, Miyaji M, Kitano T, Umehara H, Okazaki T (2004). "Expression cloning of a human cDNA restoring sphingomyelin synthesis and cell growth in sphingomyelin synthase-defective lymphoid cells". J. Biol. Chem. 279 (18): 18688–93. doi:10.1074/jbc.M401205200. PMID 14976195.
