Dengue virus (DENV) is a mosquito-borne human pathogen that causes a serious public-health threat in tropical and subtropical regions of the world. Neither a vaccine to prevent nor an effective therapeutic agent to treat DENV infection is currently available. We established a stable cell line harboring a luciferase-reporting DENV subgenomic replicon to screen for inhibitors of DENV. A total of 14,400 small-molecule (MW < 500 Da) chemicals were evaluated for their ability to reduce luciferase reporter activity in cell lysates. One effective compound was identified from the screening. This compound was found to reduce virus production but did not block virus entry in virus-based assay. Mode-of-action analysis revealed that this inhibitor suppressed viral RNA replication but did not affect replicon translation. This compound potentially could be developed as an anti-DENV agent and might be useful for dissecting the molecular mechanism of DENV replication.

The human hepatoma-derived growth factor (HDGF), containing the chromatin-associated N-terminal PWWP domain capable of binding the SMYD1 promoter, participates in various cellular processes and is involved in human cancers. We report the first crystal structures of the human HDGF PWWP domain (residues 1–100) in a complex with SMYD1 of 10 bp at 2.84 Å resolution and its apo form at 3.3 Å, respectively. The structure of the apo PWWP domain comprises mainly four β-strands and two α-helices. The PWWP domain undergoes domain swapping to dramatically transform its secondary structures, altering the overall conformation from monomeric globular folding into an extended dimeric structure upon DNA binding. The flexible loop2, as a hinge loop with the partially built structure in the apo PWWP domain, notably refolds into a visible and stable α-helix in the DNA complex. The swapped PWWP domain interacts with the minor grooves of the DNA through residues Lys19, Gly22, Arg79 and Lys80 in varied ways on loops 1 and 4 of the two chains, and the structure becomes more rigid than the apo form. These novel structural findings, together with physiological and activity assays of HDGF and the PWWP domain, provide new insights into the DNA-binding mechanism of HDGF during nucleosomal functions.

Shrimp nodaviruses, including Penaeus vannamei (PvNV) and Macrobrachium rosenbergii nodaviruses (MrNV), cause white-tail disease in shrimps, with high mortality. The viral capsid structure determines viral assembly and host specificity during infections. Here, we show cryo-EM structures of T = 3 and T = 1 PvNV-like particles (PvNV-LPs), crystal structures of the protrusion-domains (P-domains) of PvNV and MrNV, and the crystal structure of the ∆N-ARM-PvNV shell-domain (S-domain) in T = 1 subviral particles. The capsid protein of PvNV reveals five domains: the P-domain with a new jelly-roll structure forming cuboid-like spikes; the jelly-roll S-domain with two calcium ions; the linker between the S- and P-domains exhibiting new cross and parallel conformations; the N-arm interacting with nucleotides organized along icosahedral two-fold axes; and a disordered region comprising the basic N -terminal arginine-rich motif (N-ARM) interacting with RNA. The N-ARM controls T = 3 and T = 1 assemblies. Increasing the N / C -termini flexibility leads to particle polymorphism. Linker flexibility may influence the dimeric-spike arrangement.

The membrane-embedded quinol:fumarate reductase (QFR) in anaerobic bacteria catalyzes the reduction of fumarate to succinate by quinol in the anaerobic respiratory chain. The electron/proton-transfer pathways in QFRs remain controversial. Here we report the crystal structure of QFR from the anaerobic sulphate-reducing bacterium Desulfovibrio gigas (D. gigas) at 3.6 Å resolution. The structure of the D. gigas QFR is a homo-dimer, each protomer comprising two hydrophilic subunits, A and B, and one transmembrane subunit C, together with six redox cofactors including two b-hemes. One menaquinone molecule is bound near heme bL in the hydrophobic subunit C. This location of the menaquinone-binding site differs from the menaquinol-binding cavity proposed previously for QFR from Wolinella succinogenes. The observed bound menaquinone might serve as an additional redox cofactor to mediate the proton-coupled electron transport across the membrane. Armed with these structural insights, we propose electron/proton-transfer pathways in the quinol reduction of fumarate to succinate in the D. gigas QFR.