Abstract
Ddi1-like proteins are considered to belong to a family of shuttling proteins, such as Rad23 and Dsk2, that are responsible for regulation of protein degradation in ubiquitin-proteasome system. The function of protein shuttles is mediated by conserved domains-ubiquitin-like domain (UBL) targeting the proteasome and ubiquitin-associated domain (UBA) bound to the polyubiquitin chain on the substrate.
In contrast to other family members, Ddi1-like proteins harbor a retroviral protease-like domain (RVP), structurally similar to HIV protease, which contains a catalytic triad DT/SG typical for aspartic proteases. This suggests an additional role, which has not been sufficiently studied yet.
Ddi1-like proteins are highly conserved throughout eukaryotes and have an important role, as knockout experiments in yeast, worms and fruit flies propose. In S. cerevisiae, the deficiency of DDI1 gene results in deregulation of exocytosis.
Disruption of C. elegans Ddi1 gene causes defects in synaptogenesis. Ddi1 knockout in D. melanogaster induces germline cell development failure.
There are two human homologs of Ddi1-like proteins, homolog 1 (Ddi1) and homolog 2 (Ddi2), which are encoded on chromosome 11 and 1, respectively. Our project is focusing on revealing the biological role of the human Ddi2 and as it shares 96 % sequence identity with murine Ddi2, a gene knockout in mouse is an ideal model for studying the function.
We successfully generated mice with defect in the Ddi2 gene that results in embryonic lethality of homozygous individuals. This specific truncation of the protein in the RVP domain causes severe developmental defects in embryo, yolk sac and early placenta.