Seven functional classes of Barth syndrome mutation

Abstract

Patients with Barth syndrome (BTHS), a rare X-linked disease, suffer from skeletal and cardiomyopathy and bouts of cyclic neutropenia. The causative gene encodes tafazzin, a transacylase, which is the major determinant of the final acyl chain composition of the mitochondrial-specific phospholipid, CL. In addition to numerous frame shift and splice-site mutations, 36 missense mutations have been associated with BTHS. Previously, we established a BTHS-mutant panel in the yeast Saccharomyces cerevisiae that successfully models 18/21 conserved pathogenic missense mutations and defined the loss-of-function mechanism associated with a subset of the mutant tafazzins. Here, we report the biochemical and cell biological characterization of the rest of the yeast BTHS-mutant panel and in so doing identify three additional modes of tafazzin dysfunction. The largest group of mutant tafazzins is catalytically null, two mutants encode hypomorphic alleles, and another two mutants are temperature sensitive. Additionally, we have expanded the defects associated with previously characterized matrix-mislocalized-mutant tafazzins to include the rapid degradation of aggregation-prone polypeptides that correctly localize to the mitochondrial IMS. In sum, our in-depth characterization of the yeast BTHS-mutant panel has identified seven functional classes of BTHS mutation.

Unremodeled and Remodeled Cardiolipin Are Functionally Indistinguishable in Yeast

“…Great emphasis has been placed on the altered CL acyl chain composition, but Barth syndrome patients (and models) also exhibit decreased levels of CL with concurrent increases in MLCL (32)(33)(34)(35)(36)(37). Our data suggest that the absolute levels of lipids (either decreased CL or increased MLCL) and/or the absence of an active remodeling pathway may exert a larger role in contributing to the disease state than simple changes in the final acyl chain composition.…”

“…In Barth syndrome patients and models of Barth syndrome, CL levels are decreased, MLCL accumulates, and the remaining CL contains an altered acyl chain composition (32)(33)(34)(35)(36)(37), although which lipid alteration either individually or in combination leads to mitochondrial dysfunction has not been thoroughly investigated.…”

Cardiolipin fingerprinting of leukocytes by MALDI-TOF/MS as a screening tool for Barth syndrome

“…Unambiguous diagnostic testing for BTHS can be performed by determination of the relative amounts and distribution of (monolyso-)CL species and confi rmed by TAZ gene sequencing or vice versa. Unfortunately, molecular analysis of the TAZ gene can lead to false-negative results when mutations are present in regulating or relevant noncoding sequences; in addition, more than 120 distinct TAZ mutations have been described ( 4,5,36 ).…”

Natural and Induced Mitochondrial Phosphate Carrier Loss

“…The antibodies used for the yeast studies have been described previously (37)(38)(39). Images were captured with the Fluorchem Q system (Cell Biosciences, Inc.), and relative protein levels were quantified using ImageJ.…”