Parkin truncating variants result in a loss-of-function phenotype

Abstract

Parkinson disease (PD) is the second most common neurodegenerative disorder. Most cases of PD are sporadic, while 5–10% have a known genetic basis. Variants in the PARK2 gene are the most frequent cause of autosomal recessive juvenile-onset PD. PARK2 encodes parkin, a multi-domain protein that functions as an ubiquitin E3 ligase. Numerous variants spanning all parkin domains have been identified, although the pathogenic relevance for several of those remains unclear. In this study, we aimed to functionally characterize two truncating parkin variants: N52Mfs*29, which is highly prevalent in the Portuguese and Spanish populations, and L358Rfs*77, recently identified in the Portuguese population. Our results indicate that both variants are prematurely degraded by the proteasome, even though proteins levels are still moderate. We also showed that they are aggregation-prone and lead to mislocalized parkin. Interestingly, the L358Rfs*77 variant is mislocalized to the nucleus, which was never reported for parkin variants. While N52Mfs*29 impaired self-ubiquitination activity, the L358Rfs*77 variant seemed to retain it. Both variants, however, fail to ubiquitinate p62 substrate and did not relocalize to depolarized mitochondria. Therefore, we conclude that parkin truncating variants cause loss of parkin function, thus showing their causative role in PD pathogenesis.

Dopamine neuron dysfunction and loss in thePrknR275W mouse model of Juvenile Parkinsonism

“…showing that R275W mutation in PARKIN protein results in a conformational alteration 14 and lossof-function phenotype. 15 Dysfunction of SNc DA neurons in young (1-month-old) PrknR275W mice.…”

“…This is in agreement with previous studies showing that R275W mutation in PARKIN protein results in a conformational alteration 14 and loss-of-function phenotype. 15…”

“…This also agrees with previous studies showing protein conformational alteration and loss-of-function phenotype for R275W patients and for most PRKN mutations. 14,15,19 This downregulation of endogenous PARKIN levels associated with the presence of the missense PrknR275W mutation could be the reason why this model exhibits a parkinsonian phenotype, whereas Prkn KO mouse models do not. Indeed, genetic compensation is a feature of KO models but not of knockdown and mutant models.…”

Intracellular delivery of Parkin-RING0-based fragments corrects Parkin-induced mitochondrial dysfunction through interaction with SLP-2

“…PRKN variants include a wide spectrum of rearrangements and copy number variations, such as deletions and multiplications of exons, small indels, as well as single nucleotide polymorphisms causing nonsense, missense or splice site mutations [ 2 , 12 ]. Such pathogenic variants have been shown to stop the translation of a functional protein or to affect protein folding and/or protein–protein interactions and recruitment to mitochondria [ 13 , 14 ]. Parkin is a RING-in-between-RING E3 ubiquitin ligase comprising an N-terminal ubiquitin-like (Ubl) domain, followed by zinc-coordinating domains RING0 (also known as Unique Parkin Domain, UPD), RING1, an In-Between-RING (IBR) domain, a linker domain named repressor element of Parkin (REP), and the RING2 domain [ 15 , 16 ].…”

Molecular phenotypes of mitochondrial dysfunction in clinically non-manifesting heterozygous PRKN variant carriers

“…Pathogenic variants in PRKN can affect Parkin function through different mechanisms impairing its activity, stopping the translation of a functional protein, rendering the protein insoluble and enhancing aggregation, hampering protein folding and stability, and/or affecting its ability to bind to cofactors and substrates 23 . Overall, it is a complex protein exerting numerous effects, which undeniably contribute to cellular homeostasis and survival.…”