Disease mutations in the N-terminal extension and α 2'-helix of dyskerin do not abolish dimerization but disrupt binding to the telomerase RNA

The H/ACA ribonucleoprotein complex component dyskerin is essential for the biogenesis of H/ACA RNAs, including the human telomerase RNA (hTR). The N-terminal extension and 2 helix of dyskerin are hotspots for disease-associated mutations linked to X-linked dyskeratosis congenita (X-DC), a premature aging disorder. Some of these mutations disrupt dyskerin-hTR interactions, leading to hTR destabilization and reduced telomerase activity. Cryo-EM structures of human telomerase have shown that the N-terminal extension and 2 helix participate in dyskerin dimerization. However, biochemical evidence for dyskerin dimerization is still lacking, and it remains unclear whether mutations in these regions impair hTR binding by disrupting dimerization. Here, we provide the first biochemical evidence that dyskerin undergoes dimerization. We further demonstrate that dimerization is RNA independent and not abolished by disease mutations in the N-terminal extension or 2 helix. Instead, these mutations impair hTR binding. Our findings offer new mechanistic insight into how mutations in the dyskerin N-terminal extension and 2 helix contribute to the pathogenesis of X-DC.