VCP and Huntington disease: In mammalian cells, the ubiquitin ligases UBR4 and UBR5 play key roles in the formation of K11/K48 branched ubiquitin chains on misfolded and aggregation-prone proteins such as Huntington’s disease-associated HTT variant, thus allowing an enhanced binding of these modified proteins to p97/VCP complex and proteasomal substrate adaptor HHR23A.