Title : Eleven residues determine the acyl chain specificity of ceramide synthases
Abstract :
- Lipids display large structural complexity, with ∼40,000 different lipids identified to date, ∼4000 of which are sphingolipids
- A critical factor determining the biological activities of the sphingolipid, ceramide, and of more complex sphingolipids is their N-acyl chain length, which in mammals is determined by a family of six ceramide synthases (CerS)
- Little information is available about the CerS regions that determine specificity toward different acyl-CoA substrates
- We previously demonstrated that substrate specificity resides in a region of ∼150 residues in the Tram-Lag- CLN8 domain
- Using site-directed mutagenesis and biochemical analyses, we now narrow specificity down to an 11-residue sequence in a loop located between the last two putative transmembrane domains (TMDs) of the CerS
- The specificity of a chimeric protein , CerS5 (299-309→ CerS2 ), based on the backbone of CerS5 (which generates C16-ceramide), but containing 11 residues from CerS2 (which generates C22-C24 C22-C24 -ceramides), was altered such that it generated C22-C24 C22-C24 and other ceramides
- Moreover, a chimeric protein , CerS4 (291-301→ CerS2 ), based on CerS4 (which normally generates C18-C22 ceramides) displayed significant activity toward C24:1-CoA
- Additional data supported the notion that substitutions of these 11 residues alter the specificities of the CerS toward their cognate acyl-CoAs
- Our findings may suggest that this short loop may restrict adjacent TMDs, leading to a more open conformation in the membrane, and that the CerS acting on shorter acyl-CoAs may have a longer, more flexible loop, permitting TMD flexibility
- In summary, we have identified an 11-residue region that determines the acyl-CoA specificity of CerS