C-terminal oligomerization of podocin mediates interallelic interactions

Stráner, Pál and Balogh, Eszter and Schay, Gusztáv and Arrondel, Christelle and Mikó, Ágnes and L'auné, Gerda and Benmerah, Alexandre and Perczel, András and Karancsiné Menyhárd, Dóra and Antignac, Corinne and Mollet, Géraldine and Tory, Kálmán (2018) C-terminal oligomerization of podocin mediates interallelic interactions. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE, 1864. pp. 2448-2457. ISSN 0925-4439

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Abstract

Interallelic interactions of membrane proteins are not taken into account while evaluating the pathogenicity of sequence variants in autosomal recessive disorders. Podocin, a membrane-anchored component of the slit dia- phragm, is encoded by NPHS2, the major gene mutated in hereditary podocytopathies. We formerly showed that its R229Q variant is only pathogenic when trans-associated to specific 3′ mutations and suggested the causal role of an abnormal C-terminal dimerization. Here we show by FRET analysis and size exclusion chromatography that podocin oligomerization occurs exclusively through the C-terminal tail (residues 283–382): principally through the first C-terminal helical region (H1, 283–313), which forms a coiled coil as shown by circular di- chroism spectroscopy, and through the 332–348 region. We show the principal role of the oligomerization sites in mediating interallelic interactions: while the monomer-forming R286Tfs*17 podocin remains membranous irrespective of the coexpressed podocin variant identity, podocin variants with an intact H1 significantly in- fluence each other's localization (r2 = 0.68, P = 9.2 × 10 −32). The dominant negative effect resulting in in- tracellular retention of the pathogenic F344Lfs*4-R229Q heterooligomer occurs in parallel with a reduction in the FRET efficiency, suggesting the causal role of a conformational rearrangement. On the other hand, oligo- merization can also promote the membrane localization: it can prevent the endocytosis of F344Lfs*4 or F344* podocin mutants induced by C-terminal truncation. In conclusion, C-terminal oligomerization of podocin can mediate both a dominant negative effect and interallelic complementation. Interallelic interactions of NPHS2 are not restricted to the R229Q variant and have to be considered in compound heterozygous individuals.

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