Biomedical subjects
Publications and source records attributed to Thomas J Owens.
New findings (Burton et al., 2005; Kraft et al., 2005) demonstrate the direct recognition of D and KEN boxes, short sequence elements in substrates of the anaphase-promoting complex/cyclosome (APC/C), by APC/C coactivators and indicate a special role for the D box in the assembly of catalytically active APC/C.
Seismic data provide images of crust-mantle interactions during ongoing removal of the dense batholithic root beneath the southern Sierra Nevada mountains in California. The removal appears to have initiated between 10 and 3 Myr ago with a Rayleigh-Taylor-type instability, but with a pronounced asymmetric flow into a mantle downwelling (drip) beneath the adjacent Great Valley. A nearly horizontal shear zone accommodated the detachment of the ultramafic root from its granitoid batholith. With continuing flow into the mantle drip, viscous drag at the base of the remaining approximately 35-km-thick crust has thickened the crust by approximately 7 km in a narrow welt beneath the western flank of the range. Adjacent to the welt and at the top of the drip, a V-shaped cone of crust is being dragged down tens of kilometres into the core of the mantle drip, causing the disappearance of the Moho in the seismic images. Viscous coupling between the crust and mantle is therefore apparently driving present-day surface subsidence.
Transfer of conjugative plasmids between bacteria requires the activity of relaxases or mobilization proteins. These proteins nick the plasmid in a site- and strand-specific manner prior to transfer of the cut strand from donor to recipient. TraI36, the relaxase domain of TraI from plasmid F factor, binds a single-stranded DNA (ssDNA) oligonucleotide containing an F factor sequence with high affinity and sequence specificity. To better understand the energetics of this interaction, we examined the temperature, salt, and pH dependence of TraI36 recognition. Binding is entropically driven below 25 degrees C and enthalpically driven at higher temperatures. van't Hoff analysis yields an estimated deltaC(P)(0) of binding (-3300 cal x mol(-1) x K(-1)) that is larger and more negative than that observed for most double-stranded DNA (dsDNA)-binding proteins. Based on analyses of circular dichroism data and the crystal structure of the unliganded protein, we attribute the deltaC(P)(0) to both burial of hydrophobic surface area and coupled folding and binding of the protein. The salt dependence of the binding indicates that several ssDNA phosphates are buried in the complex, and the pH dependence of the binding suggests that some of these ssDNA phosphates form ionic interactions with basic residues of the protein. Although data are available for relatively few sequence-specific ssDNA-binding proteins, sufficient differences exist between TraI36 and other proteins to indicate that, like dsDNA-binding proteins, ssDNA-binding proteins use different motifs and combinations of forces to achieve specific recognition.
Although it has previously been shown that bovine parvovirus (BPV) attaches to the sialated glycoprotein glycophorin A on erythrocytes, the nature of virus-binding moieties on mammalian nucleated cells is less clear. Buffalo lung fibroblasts (Bu), primary bovine embryonic kidney cells, Madin-Darby bovine kidney cells and bovine embryonic trachea (EBTr) cells were assessed for molecules capable of binding BPV. Competition studies were carried out on both erythrocyte and nucleated cell targets using a variety of sialated compounds and sialic acid-negative compounds. Glycophorin A was found to inhibit BPV binding, while mucin exhibited low-level inhibition. These two sialated compounds also blocked attachment of BPV-modified microsphere carriers to the Bu cell membrane. Influenza A virus was used as a sialic acid competitor and interfered with BPV attachment to erythrocytes and replication in Bu cells. Significantly, the enzyme sialidase removed BPV-binding sites from Bu and EBTr cells. The binding sites could be reconstituted on sialidase-treated cells by the enzymes alpha-2,3-O-sialyltransferase and alpha-2,3-N-sialyltransferase. These results indicated that BPV can attach to sialic acid on cell membranes and that the sialylglycoproteins available for virus attachment appear to contain both N- and O-linked carbohydrate moieties, but that not all members of the sialic acid family can bind BPV. Moreover, there may be other moieties that can bind BPV, which may act as either primary or secondary receptors.