Sensitivity of the C-Terminal Nuclease Domain of Kaposi's Sarcoma-Associated Herpesvirus ORF29 to Two Classes of Active-Site Ligands.

Kaposi's sarcoma-associated herpesvirus (KSHV), the etiological agent of Kaposi's sarcoma, belongs to the Herpesviridae family, whose members employ a multicomponent terminase to resolve nonparametric viral DNA into genome-length units prior to their packaging. Homology modeling of the ORF29 C-terminal nuclease domain (pORF29C) and bacteriophage Sf6 gp2 have suggested an active site clustered with four acidic residues, D476, E550, D661, and D662, that collectively sequester the catalytic divalent metal (Mn2+) and also provided important insight into a potential inhibitor binding mode. Using this model, we have expressed, purified, and characterized the wild-type pORF29C and variants with substitutions at the proposed active-site residues. Differential scanning calorimetry demonstrated divalent metal-induced stabilization of wild-type (WT) and D661A pORF29C, consistent with which these two enzymes exhibited Mn2+-dependent nuclease activity, although the latter mutant was significantly impaired. Thermal stability of WT and D661A pORF29C was also enhanced by binding of an α-hydroxytropolone (α-HT) inhibitor shown to replace divalent metal at the active site. For the remaining mutants, thermal stability was unaffected by divalent metal or α-HT binding, supporting their role in catalysis. pORF29C nuclease activity was also inhibited by two classes of small molecules reported to inhibit HIV RNase H and integrase, both of which belong to the superfamily of nucleotidyltransferases. Finally, α-HT inhibition of KSHV replication suggests ORF29 nuclease function as an antiviral target that could be combined with latency-activating compounds as a shock-and-kill antiviral strategy.

Rare discovery of sacral "ribs": a cadaveric case report.

Supernumerary ribs are a well-documented congenital anomaly that can occur at any point of the vertebral column, most commonly in the cervical or lumbar region. However, accessory ribs found in the sacrococcygeal region are exceptionally rare and may be difficult to distinguish from other bony manifestations of the pelvic girdle. During cadaveric dissection, a pair of sacral "ribs" were found projecting from the left posterolateral sacral region. The bony projections shared a broad base from the posterior sacrum. The projections followed an anteroinferior trajectory, mimicking the thoracic rib structure. Computed tomography (CT) revealed further bony anomalies, including bilateral ossifications embedded in the sacrotuberous ligament, and a blunt bony protrusion extending toward the ischial spine. Most documented supernumerary ribs in the lumbar and sacrococcygeal regions are asymptomatic and are incidental findings in radiographic studies during the exploration of other medical complaints. Correlated symptoms mentioned in the literature include pelvic pain and decreased hip range of motion, with potential obstetric complications. Owing to their asymptomatic nature, sacral ribs may be underreported. The primary aim of this report is to provide a detailed description of these sacral "ribs" in the unique setting of a cadaveric dissection supplemented with medical imaging to enhance visualization.