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. 2011 Sep 26;111(10):6387–6422. doi: 10.1021/cr2002917

Figure 9.

Figure 9

Backbone and headgroup relational depiction of mammalian sphingolipid biosynthesis. This alternative depiction of de novo sphingolipid biosynthesis displays how the pathway can be envisioned to start with a fatty acyl-CoA (palmitoyl-CoA in lower portion of panel A) that is condensed with Ser to form 3-ketosphinganine then sphinganine (at the center of the fan), which is N-acylated to produce different chain-length dihydroceramides (represented by the ring, with examples of chain lengths labeled in blue). Each dihydroceramide subspecies can be converted into families of dihydro-complex sphingolipids, which are symbolized by the blades. The upper portion of panel A shows some of the complex sphingolipids within each wedge (which are only a fraction of the actual number of compounds that can be made, as illustrated by Figures 7 and 8, and the discussion in the text). Panel B displays further complexities related to the lipid backbones. The upper portion of panel B illustrates how the dihydroceramides from each sphingoid base backbone (in this case, d18:0 from palmitoyl-CoA) can be hydroxylated to phytoceramides (t18:0) and/or desaturated to ceramides (d18:1) (c.f., Figure 4); the latter is also presumed to undergo further desaturation to form N-acyl-sphingadienes (d18:2). The blades radiating from each N-acyl-chain subspecies represents the complex sphingolipids, as explained for panel A. The lower portion of panel B shows that Ala or Gly are alternatively used by serine palmitoyltransferase to form m18:0 and m17:0 which are N-acylated and, to some degree, desaturated to N-acyl-m18:1’s and N-acyl-m17:1 (to date, backbone hydroxylation has not been noted). Note that these do not radiate into larger blades because headgroups cannot be added. Not shown are the utilization of other fatty acyl-CoAs, which would constitute parallel schemes like these, nor pathways where sphingolipids are turned over to generate intermediates that are recycled or turned over (although one can envision this occurring within the blades to return to the hub, with the apex of the hub representing the free sphingoid base). The symbols and abbreviations are the same as have been used in the other figures in this Review.