In eukaryotic replication licensing, Cdt1 plays a key role by recruiting the MCM2-7 complex onto the origin of chromosome. The C-terminal domain of mouse Cdt1 (mCdt1C), the most conserved region in Cdt1, is essential for licensing and directly interacts with the MCM2-7 complex. We have determined the structures of mCdt1CS (mCdt1C_small; residues 452 to 557) and mCdt1CL (mCdt1C_large; residues 420 to 557) using X-ray crystallography and solution NMR spectroscopy, respectively. While the N-terminal 31 residues of mCdt1CL form a flexible loop with a short helix near the middle, the rest of mCdt1C folds into a winged helix structure. Together with the middle domain of mouse Cdt1 (mCdt1M, residues 172-368), this study reveals that Cdt1 is formed with a tandem repeat of the winged helix domain. The winged helix fold is also conserved in other licensing factors including archaeal ORC and Cdc6, which supports an idea that these replication initiators may have evolved from a common ancestor. Based on the structure of mCdt1C, in conjunction with the biochemical analysis, we propose a binding site for the MCM complex within the mCdt1C.

The DNA-dependent activator of IFN-regulatory factors (DAI), also known as DLM-1/ZBP1, initiates an innate immune response by binding to foreign DNAs in the cytosol. For full activation of the immune response, three DNA binding domains at the N terminus are required: two Z-DNA binding domains (ZBDs), Zα and Zβ, and an adjacent putative B-DNA binding domain. The crystal structure of the Zβ domain of human DAI (hZβ DAI ) in complex with Z-DNA revealed structural features distinct from other known Z-DNA binding proteins, and it was classified as a group II ZBD. To gain structural insights into the DNA binding mechanism of hZβ DAI , the solution structure of the free hZβ DAI was solved, and its bindings to B-and Z-DNAs were analyzed by NMR spectroscopy. Compared to the Z-DNA-bound structure, the conformation of free hZβ DAI has notable alterations in the α3 recognition helix, the "wing," and Y145, which are critical in Z-DNA recognition. Unlike some other Zα domains, hZβ DAI appears to have conformational flexibility, and structural adaptation is required for Z-DNA binding. Chemical-shift perturbation experiments revealed that hZβ DAI also binds weakly to B-DNA via a different binding mode. The C-terminal domain of DAI is reported to undergo a conformational change on B-DNA binding; thus, it is possible that these changes are correlated. During the innate immune response, hZβ DAI is likely to play an active role in binding to DNAs in both B and Z conformations in the recognition of foreign DNAs. DNA can activate immune responses in the innate immune system. Nonmethylated CpG sequences are recognized by toll-like receptor 9, and this results in inducing type-I interferon (IFN) (1). Double-stranded DNA, when placed in the cytosol of a cell by invading microbes or left by incomplete clearance of DNA damage, also can evoke immune responses (2-4). A recent study demonstrated that, in addition, the DNA-dependent activator of IFN-regulatory factors (DAI), formerly known as DLM-1 or ZBP1, also detects cytosolic DNAs and activates the innate immune response (5). DAI mediates activation of the innate immune system by facilitating DNA-mediated induction of type-I IFN and the expression of other related genes. DAI contains three DNA binding domains in the N terminus: two Z-DNA binding domains (ZBDs), Zα and Zβ, and an adjacent D3 region, a putative B-DNA binding domain. The D3 region plays pivotal roles in DNA binding, but all three domains are indispensable for the full activation of DAI (6). An intriguing question in innate immunity is how diverse foreign DNAs in the B-or Z-DNA conformations can be efficiently recognized by the DNA binding domains of DAI.For the last decade there have been extensive structural and biochemical studies on ZBDs. The editing enzyme ADAR1 (double-stranded RNA adenosine deaminase) was the first Zα-containing protein to be identified. Zα domains were also found in the vaccinia virus E3L protein (7) and in PKZ (protein kinase containing Z-DNA binding domain). Crystal structures of the Zα domains of A...

Promising membrane transport and separation systems for selected dicarboxylic, α-hydroxy-and α-amino acids based on thiacalixarene platform have been developed. For the first time, p-tert-butyl thiacalix [4]arenes functionalized at the lower rim with aminophosphonate fragments have been obtained and characterized. As was established by UV-vis spectroscopy, membrane extraction and HPLC, the substitution of amino groups by α-aminophosphonate units significantly enhances the selectivity of host molecules that bind to aspartic and glycolic acids. The aminophosphonate compounds synthesized can be used in the development of sensors and systems employed in the purification and separation of organic acids.

No abstract