The minichromosome maintenance protein (MCM) complex is an essential replicative helicase for DNA replication in Archaea and Eukaryotes. Whereas the eukaryotic complex consists of 6 homologous proteins (MCM2–7), the archaeon Sulfolobus solfataricus has only 1 MCM protein (ssoMCM), 6 subunits of which form a homohexamer. Here, we report a 4.35-Å crystal structure of the near-full-length ssoMCM. The structure shows an elongated fold, with 5 subdomains that are organized into 2 large N- and C-terminal domains. A near-full-length ssoMCM hexamer generated based on the 6-fold symmetry of the N-terminal Methanothermobacter thermautotrophicus (mtMCM) hexamer shows intersubunit distances suitable for bonding contacts, including the interface around the ATP pocket. Four unusual β-hairpins of each subunit are located inside the central channel or around the side channels in the hexamer. Additionally, the hexamer fits well into the double-hexamer EM map of mtMCM. Our mutational analysis of residues at the intersubunit interfaces and around the side channels demonstrates their critical roles for hexamerization and helicase function. These structural and biochemical results provide a basis for future study of the helicase mechanisms of the archaeal and eukaryotic MCM complexes in DNA replication.

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. However, there still remains a lack of effective diagnostic and therapeutic targets for this disease. Increasing evidence demonstrates that RNA modifications play an important role in the progression of HCC, but the role of the N7-methylguanosine (m7G) methylation modification in HCC has not been properly evaluated. Thus, the goal of the present study was to investigate the function and mechanism of the m7G methyltransferase WD repeat domain 4 (WDR4) in HCC as well as its clinical relevance and potential value. We first verified the high expression of WDR4 in HCC and observed that upregulated WDR4 expression increased the m7G methylation level in HCC. WDR4 promoted HCC cell proliferation by inducing the G2/M cell cycle transition and inhibiting apoptosis in addition to enhancing metastasis and sorafenib resistance through epithelial-mesenchymal transition (EMT). Furthermore, we observed that c-MYC (MYC) can activate WDR4 transcription and that WDR4 promotes CCNB1 mRNA stability and translation to enhance HCC progression. Mechanistically, we determined that WDR4 enhances CCNB1 translation by promoting the binding of EIF2A to CCNB1 mRNA. Furthermore, CCNB1 was observed to promote PI3K and AKT phosphorylation in HCC and reduce P53 protein expression by promoting P53 ubiquitination. In summary, we elucidated the MYC/WDR4/CCNB1 signalling pathway and its impact on PI3K/AKT and P53. Furthermore, the result showed that the m7G methyltransferase WDR4 is a tumour promoter in the development and progression of HCC and may act as a candidate therapeutic target in HCC treatment.

The GINS complex, which contains the four subunits Sld5, Psf1, Psf2, and Psf3, is essential for both the initiation and progression of DNA replication in eukaryotes. GINS associates with the MCM2-7 complex and Cdc45 to activate the eukaryotic minichromosome maintenance helicase. It also appears to interact with and stimulate the polymerase activities of DNA polymerase and the DNA polymerase ␣-primase complex. To further understand the functional role of GINS, we determined the crystal structure of the full-length human GINS heterotetramer. Each of the four subunits has a major domain composed of an ␣-helical bundle-like structure. With the exception of Psf1, each of the other subunits has a small domain containing a three-stranded ␤-sheet core. Each full-length protein in the crystal has unstructured regions that are all located on the surface of GINS and are probably involved in its interaction with other replication factors. The four subunits contact each other mainly through ␣-helices to form a ring-like tetramer with a central pore. This pore is partially plugged by a 16-residue peptide from the Psf3 N terminus, which is unique to some eukaryotic Psf3 proteins and is not required for tetramer formation. Removal of these N-terminal 16 residues of Psf3 from the GINS tetramer increases the opening of the pore by 80%, suggesting a mechanism by which accessibility to the pore may be regulated. The structural data presented here indicate that the GINS tetramer is a highly stable complex with multiple flexible surface regions.Cdc45 ͉ DNA helicase ͉ minichromosome maintenance complex ͉ DNA polymerase E ukaryotic DNA replication is controlled by a series of ordered and regulated steps (1-3) that commence with the binding of the six-subunit origin recognition complex (ORC) to replication origins. During the G1 phase of the cell cycle, Cdc6, and Cdt1 are recruited to the origin, and together with ORC, support the loading of the heterohexameric MCM2-7 complex (minichromosome maintenance, MCM) to form the prereplication complex (pre-RC). Although a substantial amount of data suggest that MCM acts as the replicative helicase, MCM present in the pre-RC (as well as isolated MCM) is devoid of helicase activity (summarized in ref. 4). At the G 1 /S transition of the cell cycle, it appears that the MCM helicase activity is activated by a complex and an as yet poorly understood series of modifications that require the action of two protein kinases, DDK (Cdc7-Dbf4) and CDK (cyclin-dependent), as well as the participation of at least eight additional factors, including Mcm10, Cdc45, Dpb11, GINS, synthetic lethal with dpb11 mutant-2 (Sld2), and Sld3 (4). Two of these components, Cdc45 and GINS, appear critical for helicase activation because DNA unwinding is observed (3, 5), concomitant with their loading at origins. In accord with these findings, a complex containing nearstoichiometric levels of MCM, Cdc45, and GINS was isolated from Drosophila and shown to possess DNA helicase activity (6). Studies with Xenopus extracts revealed...

Acylpeptide hydrolases (APH; also known as acylamino acid releasing enzyme) catalyze the removal of an N-acylated amino acid from blocked peptides. The crystal structure of an APH from the thermophilic archaeon Aeropyrum pernix K1 to 2.1 A resolution confirms it to be a member of the prolyl oligopeptidase family of serine proteases. The structure of apAPH is a symmetric homodimer with each subunit comprised of two domains. The N-terminal domain is a regular seven-bladed beta-propeller, while the C-terminal domain has a canonical alpha/beta hydrolase fold and includes the active site and a conserved Ser445-Asp524-His556 catalytic triad. The complex structure of apAPH with an organophosphorus substrate, p-nitrophenyl phosphate, has also been determined. The complex structure unambiguously maps out the substrate binding pocket and provides a basis for substrate recognition by apAPH. A conserved mechanism for protein degradation from archaea to mammals is suggested by the structural features of apAPH.