Novel pathogenic XK mutations in McLeod syndrome and interaction between XK protein and chorein

Abstract

ObjectiveTo identify XK pathologic mutations in 6 patients with suspected McLeod syndrome (MLS) and a possible interaction between the chorea-acanthocytosis (ChAc)- and MLS-responsible proteins: chorein and XK protein.MethodsErythrocyte membrane proteins from patients with suspected MLS and patients with ChAc, ChAc mutant carriers, and normal controls were analyzed by XK and chorein immunoblotting. We performed mutation analysis and XK immunoblotting to molecularly diagnose the patients with suspected MLS. Lysates of cultured cells were co-immunoprecipitated with anti-XK and anti-chorein antibodies.ResultsAll suspected MLS cases were molecularly diagnosed with MLS, and novel mutations were identified. The average onset age was 46.8 ± 8 years, which was older than that of the patients with ChAc. The immunoblot analysis revealed remarkably reduced chorein immunoreactivity in all patients with MLS. The immunoprecipitation analysis indicated a direct or indirect chorein-XK interaction.ConclusionsIn this study, XK pathogenic mutations were identified in all 6 MLS cases, including novel mutations. Chorein immunoreactions were significantly reduced in MLS erythrocyte membranes. In addition, we demonstrated a possible interaction between the chorein and XK protein via molecular analysis. The reduction in chorein expression is similar to that between Kell antigens and XK protein, although the chorein-XK interaction is a possibly noncovalent binding unlike the covalent Kell-XK complex. Our results suggest that reduced chorein levels following lack of XK protein are possibly associated with molecular pathogenesis in MLS.

XK is a partner for VPS13A: a molecular link between Chorea-Acanthocytosis and McLeod Syndrome

“…Because VPS13 family proteins are known to be recruited to different organelles through partner proteins, the phenotypic similarities between ChAc and McLeod Syndrome suggested that XK might be a VPS13A partner protein. This idea is strongly supported by the fact that the two proteins form a complex and colocalize within the cell ( Urata et al , 2019 ; this work). Furthermore, XK is capable of relocalizing VPS13A from lipid droplets to ER subdomains, and two different disease-associated mutations in VPS13A disrupt this relocalization.…”

“…Coimmunoprecipitation was also observed when the situation was reversed, that is, GFP-XK, but not GFP alone, was detected in immunoprecipitates generated using α-VPS13A antibodies ( Figure 1C ). Coimmunoprecipitation of VPS13A and XK was independently discovered by Urata et al (2019) . XK and VPS13A therefore form a complex in vivo.…”

Disposition of Proteins and Lipids in Synaptic Membrane Compartments Is Altered in Q175/Q7 Huntington’s Disease Mouse Striatum

“…Although the levels of these proteins were all reduced in total signal on the western blots of fractions from Q175 compared to wild-type, their peak distribution was in lower fractions (3–7) and no shift in their percent distribution in the gradient occurred. We also looked at XK, a protein that when mutated produces chorea ( Jung et al, 2003 ; Urata et al, 2019 ) and found no change in levels or distribution occurred in fractionations for XK for Q175/Q7 HD compared to Q7/Q7 striatum.…”

“…We also looked at XK, a protein that when mutated produces chorea (Jung et al, 2003;Urata et al, 2019) and found no change in levels or distribution occurred in fractionations for XK for Q175/Q7 HD compared to Q7/Q7 striatum.…”

Insights into VPS13 properties and function reveal a new mechanism of eukaryotic lipid transport

“…It is therefore of interest that XK is a paralogue of proteins with scrambling activity, although a scrambling function for XK itself remains to be proven [ 61 ]. Notably, cell-based overexpression studies have suggested a physical interaction between XK and VPS13A [ 60 ] and, consistently, reduced levels of VPS13A have been reported in McLeod patients [ 110 ]. However, as the bulk of XK is thought to be primarily localized at the plasma membrane, the functional connection between these two proteins remains to be further explored.…”