7k0p
Human serine palmitoyltransferase complex SPTLC1/SPLTC2/ssSPTa/ORMDL3, class 4
Structural highlights
DiseaseSPTC1_HUMAN Hereditary sensory and autonomic neuropathy type 1;Juvenile amyotrophic lateral sclerosis. The disease is caused by variants affecting the gene represented in this entry. Variants associated with ALS27 tend to disrupt the normal homeostatic regulation of serine palmitoyltransferase (SPT) by ORMDL proteins, resulting in up-regulated SPT activity and elevated levels of canonical SPT products.[1] The disease is caused by variants affecting the gene represented in this entry. Variants associated with HSAN1A tend to increase serine palmitoyltransferase (SPT) usage of alanine or glycine rather than serine, resulting in deoxysphingolipid synthesis. Deoxysphingolipids cannot be efficiently degraded by the cell machinery and cause cell toxicity.[2] FunctionSPTC1_HUMAN Component of the serine palmitoyltransferase multisubunit enzyme (SPT) that catalyzes the initial and rate-limiting step in sphingolipid biosynthesis by condensing L-serine and activated acyl-CoA (most commonly palmitoyl-CoA) to form long-chain bases. The SPT complex is also composed of SPTLC2 or SPTLC3 and SPTSSA or SPTSSB. Within this complex, the heterodimer with SPTLC2 or SPTLC3 forms the catalytic core (PubMed:19416851, PubMed:33558762, PubMed:36170811). The composition of the serine palmitoyltransferase (SPT) complex determines the substrate preference (PubMed:19416851, PubMed:33558762). The SPTLC1-SPTLC2-SPTSSA complex shows a strong preference for C16-CoA substrate, while the SPTLC1-SPTLC3-SPTSSA isozyme uses both C14-CoA and C16-CoA as substrates, with a slight preference for C14-CoA (PubMed:19416851, PubMed:19648650). The SPTLC1-SPTLC2-SPTSSB complex shows a strong preference for C18-CoA substrate, while the SPTLC1-SPTLC3-SPTSSB isozyme displays an ability to use a broader range of acyl-CoAs, without apparent preference (PubMed:19416851, PubMed:19648650, PubMed:33558761, PubMed:33558762). Required for adipocyte cell viability and metabolic homeostasis (By similarity).[UniProtKB:O35704][3] [4] [5] [6] [7] Publication Abstract from PubMedSphingolipids are essential lipids in eukaryotic membranes. In humans, the first and rate-limiting step of sphingolipid synthesis is catalyzed by the serine palmitoyltransferase holocomplex, which consists of catalytic components (SPTLC1 and SPTLC2) and regulatory components (ssSPTa and ORMDL3). However, the assembly, substrate processing and regulation of the complex are unclear. Here, we present 8 cryo-electron microscopy structures of the human serine palmitoyltransferase holocomplex in various functional states at resolutions of 2.6-3.4 A. The structures reveal not only how catalytic components recognize the substrate, but also how regulatory components modulate the substrate-binding tunnel to control enzyme activity: ssSPTa engages SPTLC2 and shapes the tunnel to determine substrate specificity. ORMDL3 blocks the tunnel and competes with substrate binding through its amino terminus. These findings provide mechanistic insights into sphingolipid biogenesis governed by the serine palmitoyltransferase complex. , PMID:33558761[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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