Crystal structure of the 3-ketodihydrosphingosine reductase TSC10 from Cryptococcus neoformans

The second step in the de novo sphingolipid biosynthesis is the reduction of 3-ketodihydrosphingosine by 3-ketodihydrosphingosine reductase (KDSR) to produce dihydrosphingosine (sphinganine). Fungal TSC10 and mammalian KDSR (also named FVT-1) proteins are the enzymes responsible for this process and they belong to the short-chain dehydrogenase/reductase (SDR) superfamily. Albeit that both fungal and mammalian 3-ketodihydrosphingosine reductases were identified more than a decade ago, no structure of these enzymes from any species has been experimentally determined. Here we report the crystal structure of the catalytic domain of TSC10 from Cryptococcus neoformans in complex with NADPH. cnTSC10 adopts a Rossmann fold with a central seven-stranded β-sheet flanked by α-helices on both sides. Several regions are disordered that include the segment connecting the serine and tyrosine residues of the catalytic triad, the so-called 'substrate loop', and the C-terminal region that often participates in homo-tetramerization in other SDRs. In addition, the cofactor NADPH is not fully ordered. These structural features indicate that the catalytic site of cnTSC10 possesses significant flexibility. cnTSC10 is predominantly dimeric in solution while a minor portion of the protein forms homo-tetramer. The crystal structure reveals that the homo-dimer interface involves both hydrophobic and hydrophilic interactions mediated by helices α4 and α5, as well as the loop connecting strand β4 and helix α4. Because residues forming hydrogen bonds and salt bridges in the dimer interface are not conserved between fungal TSC10 and mammalian KDSR proteins, it might be possible to develop inhibitors that selectively target fungal TSC10 dimerization.

Case report: Compound heterozygous mutations in the KDSR gene cause progressive keratodermia and thrombocytopenia

KDSR (3-ketodihydrosphingosine reductase) is a short-chain dehydrogenase located in the endoplasmic reticulum. Mutations in KDSR cause defects in ceramides, which play a key role in the biological processes of the skin and other tissues. Herein, we report a case of compound heterozygous mutations in KDSR that caused progressive keratodermia and thrombocytopenia in a 2-year-old male patient.

Mutations in KDSR Cause Recessive Progressive Symmetric Erythrokeratoderma

The discovery of new genetic determinants of inherited skin disorders has been instrumental to the understanding of epidermal function, differentiation, and renewal. Here, we show that mutations in KDSR (3-ketodihydrosphingosine reductase), encoding an enzyme in the ceramide synthesis pathway, lead to a previously undescribed recessive Mendelian disorder in the progressive symmetric erythrokeratoderma spectrum. This disorder is characterized by severe lesions of thick scaly skin on the face and genitals and thickened, red, and scaly skin on the hands and feet. Although exome sequencing revealed several of the KDSR mutations, we employed genome sequencing to discover a pathogenic 346 kb inversion in multiple probands, and cDNA sequencing and a splicing assay established that two mutations, including a recurrent silent third base change, cause exon skipping. Immunohistochemistry and yeast complementation studies demonstrated that the mutations cause defects in KDSR function. Systemic isotretinoin therapy has achieved nearly complete resolution in the two probands in whom it has been applied, consistent with the effects of retinoic acid on alternative pathways for ceramide generation.