Deoxyribonucleic acid (DNA) has been hypothesized to act as a molecular wire due to the presence of an extended π-stack between base pairs, but the factors that are detrimental in the mechanism of charge transport (CT) across tunnel junctions with DNA are still unclear. Here we systematically investigate CT across dense DNA monolayers in large-area biomolecular tunnel junctions to determine when intrachain or interchain CT dominates and under which conditions the mechanism of CT becomes thermally activated. In our junctions, double-stranded DNA (dsDNA) is 30-fold more conductive than single-stranded DNA (ssDNA). The main reason for this large change in conductivity is that dsDNA forms ordered monolayers where intrachain tunneling dominates, resulting in high CT rates. By varying the temperature T and the length of the DNA fragments in the junctions, which determines the tunneling distance, we reveal a complex interplay between T, the length of DNA, and structural order on the mechanism of charge transport. Both the increase in the tunneling distance and the decrease in structural order result in a change in the mechanism of CT from coherent tunneling to incoherent tunneling (hopping). Our results highlight the importance of the interplay between structural order, tunneling distance, and temperature on the CT mechanism across DNA in molecular junctions.
Galectin‐1 (Gal‐1), a protein that impacts the fate and function of immune cells known to fight infection, eliminates cancer, and promotes inflammation, is found in most mammalian tissues at low levels. A small 130 amino acid “jelly‐roll” shaped ß‐galactoside‐binding lectin with a hydrophobic core, Gal‐1 plays a role in controlling intracellular processes, such as cell cycle progression and cell proliferation. Gal‐1 binds with high affinity to glycoconjugates galactose (Gal) and N‐acetylglucosamine (GlcNAc) by van der Waals forces and hydrogen bonding via a highly conserved carbohydrate recognition domain. Because native Gal‐1 oxidizes rapidly and loses its carbohydrate‐binding activity, studying the effect of Gal‐1 has been difficult. The Dimitroff laboratory engineered a Gal‐1 – human immunoglobulin Fc chimeric molecule (Gal‐1hFc), which facilitates dimerization while preventing oxidation‐induced multimerization. Experimental evidence has demonstrated that Gal‐1hFc behaves like native Gal‐1, enabling the use of the chimera to study Gal‐1’s effect on immune responses. The Governor’s Academy SMART (Students Modeling A Research Topic) Team designed a model using 3D printing technology to provide further evidence of Gal‐1hFc’s structure and binding function. Grant Funding Source: Supported by grants from NIH‐CTSA UL1RR031973 and NIH/NCI RO1CA118124
Helicases are highly conserved enzymes that unwind the double helix of DNA, providing access to single‐stranded DNA. Found in all living organisms and viruses, helicases function as motor proteins in replication, transcription, and remodeling of DNA. A common sexually‐transmitted oncovirus, human papillomavirus (HPV) uses E1 helicase, the most studied helicase protein because of the ease by which it can be isolated. The only enzyme encoded in the HPV episome, E1 hexameric helicase is a ring‐shaped translocase that belongs to the AAA+ family and superfamily 3. E1 has near exact rotational symmetry with respect to its six subunits. Each monomer comprises a central five‐stranded anti‐parallel beta‐sheet and six alpha helices. Conserved sequence motifs Walker A and B and an arginine finger participate in the binding and hydrolysis of ATP causing conformational changes in β‐hairpins, powering the walking movement along the ssDNA. Assembling first as a double‐trimer at the replication origin and then into two homohexamers on opposing strands, E1 separates the dsDNA into ssDNA by occlusion in the 3'→5' direction. Asymmetric sequential progression of ATP hydrolysis around the hexameric ring at catalytic sites between monomers powers translocation of E1. An understanding of its functional domains and how they interact with each other, DNA, and host proteins is necessary to elucidate the overall mechanism of helicase function. Using 3D printing technology, The Governor's Academy SMART (Students Modeling A Research Topic) Team modeled the E1 helicase to provide vital insight into the mechanism of eukaryotic DNA replication and potentially promote development of therapeutic treatments.
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