Mutations in the mitochondrial thioredoxin reductase gene TXNRD2 cause dilated cardiomyopathy.

AIMS: Cardiac energy requirement is met to a large extent by oxidative phosphorylation in mitochondria that are highly abundant in cardiac myocytes. Human mitochondrial thioredoxin reductase (TXNRD2) is a selenocysteine-containing enzyme essential for mitochondrial oxygen radical scavenging. Cardiac-specific deletion of Txnrd2 in mice results in dilated cardiomyopathy (DCM). The aim of this study was to investigate whether TXNRD2 mutations explain a fraction of monogenic DCM cases. METHODS AND RESULTS: Sequencing and subsequent genotyping of TXNRD2 in patients diagnosed with DCM (n = 227) and in DCM-free (n = 683) individuals from the general population sample KORA S4 was performed. The functional impact of observed mutations on Txnrd2 function was tested in mouse fibroblasts. We identified two novel amino acid residue-altering TXNRD2 mutations [175G > A (Ala59Thr) and 1124G > A (Gly375Arg)] in three heterozygous carriers among 227 patients that were not observed in the 683 DCM-free individuals. Both DCM-associated mutations result in amino acid substitutions of highly conserved residues in helices contributing to the flavin-adenine dinucleotide (FAD)-binding domain of TXNRD2. Functional analysis of both mutations in Txnrd2(-/-) mouse fibroblasts revealed that contrasting to wild-type (wt) Txnrd2, neither mutant did restore Txnrd2 function. Mutants even impaired the survival of Txnrd2 wt cells under oxidative stress by a dominant-negative mechanism. CONCLUSION: For the first time, we describe mutations in DCM patients in a gene involved in the regulation of cellular redox state. TXNRD2 mutations may explain a fraction of human DCM disease burden.

UBXD1 binds p97 through two independent binding sites.

The chaperone-related p97 protein plays a central role in various cellular processes involving the ubiquitin-proteasome system. The diverse functions of p97 are controlled by a large number of cofactors that recruit specific substrates or influence their ubiquitylation state. Many cofactors bind through a UBX or PUB domain, two major p97 binding modules. However, the recently identified UBXD1 cofactor possesses both domains. To elucidate the molecular basis underlying the interaction between UBXD1 and p97, we analyzed the contribution of both domains to p97 binding biochemically and in living cells. The PUB domain mediated robust binding to the carboxy-terminus of p97, while the UBX domain did not contribute to p97 binding. Importantly, we identified an additional p97 binding site in UBXD1 that competed with the p47 cofactor for binding to the N domain of p97. This novel, bipartite binding mode suggests that UBXD1 could be an efficient regulator of p97 cofactor interactions.