A complex comprising C15ORF41 and Codanin-1: the products of two genes mutated in congenital dyserythropoietic anaemia type I (CDA-I)

Congenital dyserythropoietic anaemia (CDA) type I is a rare blood disorder characterised by moderate to severe macrocytic anaemia and hepatomegaly, with spongy heterochromatin and inter-nuclear bridges seen in bone marrow erythroblasts. The vast majority of cases of CDA type I are caused by mutations in the CDAN1 gene. The product of CDAN1 is Codanin-1, which interacts the histone chaperone ASF1 in the cytoplasm. Codanin-1 is a negative regulator of chromatin replication, sequestering ASF1 in the cytoplasm, restraining histone deposition and thereby limiting DNA replication. The remainder of CDA-I cases are caused by mutations in the C15ORF41 gene, but very little is known about the product of this gene. Here, we report that C15ORF41 forms a tight, near-stoichiometric complex with Codanin1 in human cells, interacting with the C-terminal region of Codanin-1. We present the characterisation of the C15ORF41–Codanin-1 complex in humans in cells and in vitro, and demonstrate that Codanin-1 appears to sequester C15ORF41 in the cytoplasm as previously shown for ASF1. The findings in this study have major implications for understanding the functions of C15ORF41 and Codanin-1, and the aetiology of CDA-I.

Ubiquitin stimulated reversal of topoisomerase 2 DNA-protein crosslinks by TDP2

Tyrosyl-DNA phosphodiesterase 2 (TDP2) reverses Topoisomerase 2 DNA–protein crosslinks (TOP2-DPCs) in a direct-reversal pathway licensed by ZATTZNF451 SUMO2 E3 ligase and SUMOylation of TOP2. TDP2 also binds ubiquitin (Ub), but how Ub regulates TDP2 functions is unknown. Here, we show that TDP2 co-purifies with K63 and K27 poly-Ubiquitinated cellular proteins independently of, and separately from SUMOylated TOP2 complexes. Poly-ubiquitin chains of ≥ Ub3 stimulate TDP2 catalytic activity in nuclear extracts and enhance TDP2 binding of DNA–protein crosslinks in vitro. X-ray crystal structures and small-angle X-ray scattering analysis of TDP2-Ub complexes reveal that the TDP2 UBA domain binds K63-Ub3 in a 1:1 stoichiometric complex that relieves a UBA-regulated autoinhibitory state of TDP2. Our data indicates that that poly-Ub regulates TDP2-catalyzed TOP2-DPC removal, and TDP2 single nucleotide polymorphisms can disrupt the TDP2-Ubiquitin interface.

Direct and essential function for Hrd3 in ER-associated degradation

The HRD (HMG-CoA reductase degradation) pathway is a conserved route of endoplasmic reticulum-associated degradation (ERAD), by which misfolded ER proteins are ubiquitinated and degraded. ERAD substrates are ubiquitinated by the action of the Hrd1 RING-H2 E3 ligase. Hrd1 is always present in a stoichiometric complex with the ER membrane protein Hrd3, which is also required for HRD-dependent degradation. Despite its conserved presence, unequivocal study of Hrd3 function has been precluded by its central role in Hrd1 stability. Loss of Hrd3 causes unrestricted self-degradation of Hrd1, resulting in significant loss of the core ligase. Accordingly, the degree to which Hrd3 functions independently of Hrd1 stabilization has remained unresolved. By capitalizing on our studies of Usa1 in Hrd1 degradation, we have devised a new approach to evaluate Hrd3 functions in ERAD. We now show that Hrd3 has a direct and critical role in ERAD in addition to Hrd1 stabilization. This direct component of Hrd3 is phenotypically as important as Hrd1 in the native HRD complex. Hrd3 was required the E3 activity of Hrd1, rather than substrate or E2 recruitment to Hrd1. Although Hrd1 can function in some circumstances independent of Hrd3, these studies show an indispensable role for Hrd3 in living cells.

A Lawsone–DAMN based colorimetric chemosensor for rapid naked-eye detection of mercury(ii)

A highly sensitive and selective chemosensorLexhibited well-defined naked-eye visible color changes from yellow to pink, which was used for Hg2+detection in acetonitrile. For the selective recognition of Hg2+ions, it forms a 1 : 1 stoichiometric complex involving naphthoquinone hydroxyl and diaminomaleonitrile nitrogen functionalities.

The Zds proteins control entry into mitosis and target protein phosphatase 2A to the Cdc25 phosphatase

The Wee1 kinase restrains entry into mitosis by phosphorylating and inhibiting cyclin-dependent kinase 1 (Cdk1). The Cdc25 phosphatase promotes entry into mitosis by removing Cdk1 inhibitory phosphorylation. Experiments in diverse systems have established that Wee1 and Cdc25 are regulated by protein phosphatase 2A (PP2A), but a full understanding of the function and regulation of PP2A in entry into mitosis has remained elusive. In budding yeast, entry into mitosis is controlled by a specific form of PP2A that is associated with the Cdc55 regulatory subunit (PP2ACdc55). We show here that related proteins called Zds1 and Zds2 form a tight stoichiometric complex with PP2ACdc55and target its activity to Cdc25 but not to Wee1. Conditional inactivation of the Zds proteins revealed that their function is required primarily at entry into mitosis. In addition, Zds1 undergoes cell cycle–dependent changes in phosphorylation. Together, these observations define a role for the Zds proteins in controlling specific functions of PP2ACdc55and suggest that upstream signals that regulate PP2ACdc55may play an important role in controlling entry into mitosis.