Mutations in NPC1 Highlight a Conserved NPC1-Specific Cysteine-Rich Domain

Abstract

Niemann-Pick type II disease is an autosomal recessive disorder characterized by a defect in intracellular trafficking of sterols. We have determined the intron/exon boundaries of eight exons from the conserved 3' portion of NPC1, the gene associated with most cases of the disease. SSCP analyses were designed for these exons and were used to identify the majority of mutations in 13 apparently unrelated families. Thirteen mutations were found, accounting for 19 of the 26 alleles. These mutations included eight different missense mutations (including one reported by Greer et al. [1998]), one 4-bp and two 2-bp deletions that generate premature stop codons, and two intronic mutations that are predicted to alter splicing. Two of the missense mutations were present in predicted transmembrane (TM) domains. Clustering of these and other reported NPC1 mutations in the carboxy-terminal third of the protein indicates that screening of these exons, by means of the SSCP analyses reported here, will detect most mutations. The carboxy-terminal half of the Npc1 protein shares amino acid similarity with the TM domains of the morphogen receptor Patched, with the largest stretch of unrelated sequence lying between two putative TM spans. Alignment of this portion of the human Npc1 protein sequence with Npc1-related sequences from mouse, yeast, nematode, and a plant, Arabidopsis, revealed conserved cysteine residues that may coordinate the structure of this domain. That 7 of a total of 13 NPC1 missense mutations are concentrated in this single Npc1-specific domain suggests that integrity of this region is particularly critical for normal functioning of the protein.

The Spectrum of Niemann-Pick Type C Disease in Greece

“…In our cohort of patients the mutation was also identified either in homozygosity or heterozygosity in three patients all with the variant filipin staining pattern. In homozygosity it was associated with the adult form of the disease in siblings #12 and #13, in good accordance with other studies (Ribeiro et al 2001;Stampfer et al 2013) whereas in heterozygosity with the missense mutation p.S940L(c.2819C>T) (Greer et al 1999) it was associated with juvenile onset of disease (Patient #11). Patient #14 was shown to be homozygous for the mutation IVS2+5G>A (c.190+5G>A) in the NPC2 gene.…”

“…In the NPC1 patients, 12 different mutations and nine different genotypes were identified. Eight of the mutations had been previously described: p.E1089K (3265G>A) (Sun et al 2001), p.F284Lfs*26 (c.852delT) (Fancello et al 2009), p. A1132P(c.3394G>C) (Mavridou et al 2014), del promoter region and exons 1-10 (Rodriguez-Pascau et al 2012), p. R1186H(c.3557G>A) (Carstea et al 1997), p.P1007A (c.3019C>G) (Greer et al 1999), p.Q92R(c.275A>G) (Ribeiro et al 2001), and p.S940L(c.2819C>T) (Greer et al 1999). The mutations p.A1132P(c.3394G>C) and the large deletion of the promoter region and of exons 1-10 have only been described in Greek patients (included in this report as #2, #3, #7).…”

Niemann–Pick Type C Mutations Cause Lipid Traffic Jam

“…The cysteine-rich hydrophilic loop (aa 857-1015) is drawn oriented toward the organelle lumen. This follows the reasoning of Greer et al (35) that the corresponding Patched loop must be extracellular, as it binds the secreted signaling molecule Sonic hedgehog (38).…”

“…As noted by Greer et al (35), the third carboxy-terminal of NPC1 harbors 19 of the 21 reported human gene mutations (11,24,35). Seven of the 13 reported missense mutations are clustered within an 88 amino acid stretch (aa 927-1015) of the cysteine-rich domain.…”

3.3 Å structure of Niemann–Pick C1 protein reveals insights into the function of the C-terminal luminal domain in cholesterol transport

“…1 C and D). As suggested by its other name, "cysteine-rich domain" (24), the CTD contains eight cysteines. All cysteine residues form four pairs of disulfide bonds to stabilize the loops on the tip of this domain ( Fig.…”