Nonsense and temperature-sensitive mutations in PEX13 are the cause of complementation group H of peroxisome biogenesis disorders

Abstract

Peroxisome biogenesis disorders, including Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease, are lethal hereditary diseases caused by abnormalities in peroxisomal assembly. To date, 12 genotypes have been identified. We now have evidence that the complete human cDNA encoding Pex13p, an SH3 protein of a docking factor for the peroxisome targeting signal 1 receptor (Pex5p), rescues peroxisomal matrix protein import and its assembly in fibroblasts from PBD patients of complementation group H. In addition, we detected mutations on the human PEX13 cDNA in two patients of group H. A severe phenotype of a ZS patient (H-02) was homozygous for a nonsense mutation, W234ter, which results in the loss of not only the SH3 domain but also the putative transmembrane domain of Pex13p. A more mildly affected NALD patient (H-01), whose fibroblasts showed the temperature-sensitive (TS) phenotype, was homozygous for a missense mutation in the SH3 domain of Pex13p, I326T. This mutant PEX13 cDNA expression in a PEX13-defective CHO mutant showed I326T to be a TS mutation and thus suggested that Pex13p with the I326T mutation in the SH3 domain is stable at 30 degrees C but is somewhat unstable at 37 degrees C.

Temperature-Sensitive Mutation of PEX6 in Peroxisome Biogenesis Disorders in Complementation Group C (CG-C): Comparative Study of PEX6 and PEX1

“…In previous studies, we revealed the restoration of peroxisomes in a temperature-dependent manner in the fibroblasts of patients with milder types of PBD, those with all types of IRD, and some with the NALD phenotype in CG-E (CG1), CG-A (CG8), CG-F (CG10), and CG-H. In addition, we demonstrated ts mutations that cause this phenomenon in IRD and NALD patients with CG-E (CG1), CG-F (CG10), and CG-H; G843D in PEX1, E55K in PEX2, and I326T in PEX13, respectively (18,23,24). We have now identified a missense mutation in PEX6 from a NALD patient with CG-C (CG4) whose fibroblasts revealed the same ts phenotype.…”

“…In humans, defective peroxisomal metabolic functions result in ZS, NALD, and IRD, collectively referred to as PBD, which are genetically classified into at least 12 CG (2). Ten causative genes (PEX) have been cloned: PEX1, PEX2, PEX5, PEX6, PEX7, PEX10, PEX12, PEX13, PEX16, and PEX19, corresponding with CG-E (CG1), CG-F (CG10), CG2, CG-C (CG4), CG11, CG-B (CG7), CG3, CG-H, CG-D (CG9), and CG-J in humans, respectively (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). ZS patients have profound dysmorphic features, skeletal abnormalities, renal cysts, and severe progressive neurologic and hepatic disease and, therefore, rarely survive early infancy.…”

Molecular Mechanism of a Temperature-Sensitive Phenotype in Peroxisomal Biogenesis Disorder

“…Biochemical analyses including fatty acids indicated peroxisomal abnormalities (C24:0/ C16:0: 0.15; normal control: 0.58), but dihydroxyacetone phosphate acyltransferase activity was normal in the patient's fibroblasts (patient: 2.26; control: 1.55 nmol/mg/120 min) (8).…”

“…The patient with the milder form, NALD, had a missense mutation with substitution of isoleucine (Ile) 326 by threonine (Thr), I326T, within a SH3 domain, and showed normal development just before a sudden deterioration with a high fever due to a respiratory infection. Additionally, the patient's fibroblasts showed a TS phenotype in peroxisome assembly and function (8).…”

“…Pex13p is a peroxisomal membrane protein containing an SH3, which typically requires the PxxP motif for its binding partners, as observed in Pex14p (6,7). Mutation analysis of PEX13 revealed that two patients belonging to complementation group H with the ZS and NALD phenotypes carried a nonsense and a missense mutation, respectively (8). The patient with the milder form, NALD, had a missense mutation with substitution of isoleucine (Ile) 326 by threonine (Thr), I326T, within a SH3 domain, and showed normal development just before a sudden deterioration with a high fever due to a respiratory infection.…”