Species B human adenoviruses (Ads) are often associated with fatal illnesses in immunocompromised individuals. Recently, species B Ads, most of which use the ubiquitously expressed complement regulatory protein CD46 as a primary attachment receptor, have gained interest for use as gene therapy vectors. In this study, we focused on species B Ad serotype 35 (Ad35), whose trimeric fiber knob domain binds to three CD46 molecules with a K D (equilibrium dissociation constant) of 15.5 nM. To study the Ad35 knob-CD46 interaction, we generated an expression library of Ad35 knobs with random mutations and screened it for CD46 binding. We identified four critical residues (Phe242, Arg279, Ser282, and Glu302) which, when mutated, ablated Ad35 knob binding to CD46 without affecting knob trimerization. The functional importance of the identified residues was validated in surface plasmon resonance and competition binding studies. To model the Ad35 knob-CD46 interaction, we resolved the Ad35 knob structure at 2-Å resolution by X-ray crystallography and overlaid it onto the existing structure for Ad11-CD46 interaction. According to our model, all identified Ad35 residues are in regions that interact with CD46, whereby one CD46 molecule binds between two knob monomers. This mode of interaction might have potential consequences for CD46 signaling and intracellular trafficking of Ad35. Our findings are also fundamental for better characterization of species B Ads and design of antiviral drugs, as well as for application of species B Ads as in vivo and in vitro gene transfer vectors.

We study the surface crystalline and electronic structures of the antiferromagnetic topological insulator MnBi2Te4 using scanning tunneling microscopy/spectroscopy (STM/S), micro(μ)-laser angle-resolved photoemission spectroscopy (ARPES), and density functional theory calculations. Our STM images reveal native point defects at the surface that we identify as BiTe antisites and MnBi substitutions. Bulk X-ray diffraction further evidences the presence of the Mn-Bi intermixing. Overall, our characterizations suggest that the defects concentration is nonuniform within crystals and differs from sample to sample. Consistently, the ARPES and STS experiments reveal that the Dirac point gap of the topological surface state is different for different samples and sample cleavages, respectively. Our calculations show that the antiparallel alignment of the MnBi moments with respect to those of the Mn layer can indeed cause a strong reduction of the Dirac point gap size. The present study provides important insights into a highly debated issue of the MnBi2Te4 Dirac point gap.

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The Rana catesbeiana (bullfrog) ribonucleases, which belong to the RNase A superfamily, exert cytotoxicity toward tumor cells. RC-RNase, the most active among frog ribonucleases, has a unique base preference for pyrimidine-guanine rather than pyrimidine-adenine in RNase A. Residues of RC-RNase involved in base specificity and catalytic activity were determined by sitedirected mutagenesis, k cat /K m analysis toward dinucleotides, and cleavage site analysis of RNA substrate. The results show that Pyr-1 (N-terminal pyroglutamate), Lys-9, and Asn-38 along with His-10, Lys-35, and His-103 are involved in catalytic activity, whereas Pyr-1, Thr-39, Thr-70, Lys-95, and Glu-97 are involved in base specificity. The cytotoxicity of RC-RNase is correlated, but not proportional to, its catalytic activity. The crystal structure of the RC-RNase⅐d(ACGA) complex was determined at 1.80 Å resolution. Residues Lys-9, His-10, Lys-35, and His-103 interacted directly with catalytic phosphate at the P 1 site, and Lys-9 was stabilized by hydrogen bonds contributed by Pyr-1, Tyr-28, and Asn-38. Thr-70 acts as a hydrogen bond donor for cytosine through Thr-39 and determines B 1 base specificity. Interestingly, Pyr-1 along with Lys-95 and Glu-97 form four hydrogen bonds with guanine at B 2 site and determine B 2 base specificity.Ribonucleases are found widely within living organisms and are thought to play an important role in the metabolism of RNA. Recently, it has been shown that several members of the bovine ribonuclease superfamily exhibit biological functions in addition to intrinsic ribonucleolytic activities. Human eosinophil-derived neurotoxin and eosinophil cationic protein exert neurotoxicity (1) as well as antiparasitic activity (2), human angiogenin induces blood vessel formation (3), and frog ribonuclease exhibits antitumor activity (4, 5). Ribonucleolytic activity is essential for the biological functions of these proteins (6 -12).Bovine pancreatic ribonuclease, known as RNase A, in the ribonuclease superfamily is well characterized and is a valuable model for the study of structure-function relationships and protein refolding (13,14). It consists of 124 amino acid residues linked with four pairs of disulfide bridges and possesses a substrate preference for pyrimidine-adenosine in the RNA sequence but no cytotoxicity toward tumor cells. There are three subsites within RNase A molecule: the P 1 site, at which phosphodiester bond cleavage occurs; the B 1 site, for binding pyrimidine, which donates oxygen via its ribose to the scissile bond; and the B 2 site, for binding the adenine ring on the opposite site of the scissile bond. Three amino acid residues, His-12, Lys-41, and His-119, at the P 1 site are involved in catalytic activity. Four amino acid residues, Thr-45, Asp-83, Phe-120, and Ser-123, at the B 1 site are involved in the binding of the 5Ј-ribonucleoside, pyrimidine, whereas two residues, Asn-71 and Glu-111, at the B 2 site are involved in the binding of the 3Ј-ribonucleoside, adenosine (14 -18).A new group of ribon...