Would Self-Expanding Stent Occlude Middle Cerebral Artery Perforators?

Background and Purpose— A major concern of intracranial stenting is perforator infarction. It is unclear whether the sustained radial force of a self-expanding stent or subsequent stent restenosis would cause late occlusion of perforators.

Methods— We compared the baseline and poststent (≥4 months) MRI scans of patients who underwent self-expanding stenting for recurrent ischemic symptoms attributed to a MCA stenosis ≥60%. New infarcts in the ipsilateral striatocapsular region were recorded.

Results— MCA stenting was technically successful in 23 of 24 recruited patients. No new perforator territory infarct was found in follow-up MRI scans of all recruited patients. Postoperatively, all patients reported no further TIA or stroke over a median follow-up of 15 months.

Conclusions— The use of a self-expanding stent in patients with high-grade MCA stenosis may not pose a major risk to the perforators.

Cold-plasma modification of oxide surfaces for covalent biomolecule attachment

While many processes have been developed to modify the surface of glass and other oxides for biomolecule attachment, they rely primarily upon wet chemistry and are costly and time-consuming. We describe a process that uses a cold plasma and a subsequent in vacuo vapor-phase reaction to terminate a variety of oxide surfaces with epoxide chemical groups. These epoxide groups can react with amine-containing biomolecules, such as proteins and modified oligonucleotides, to form strong covalent linkages between the biomolecules and the treated surface. The use of a plasma activation step followed by an in vacuo vapor-phase reaction allows for the precise control of surface functional groups, rather than the mixture of functionalities normally produced. By maintaining the samples under vacuum throughout the process, adsorption of contaminants is effectively eliminated. This process modifies a range of different oxide surfaces, is fast, consumes a minimal amount of reagents, and produces attachment densities for bound biomolecules that are comparable to or better than commercially available substrates.

Base excision and DNA binding activities of human alkyladenine DNA glycosylase are sensitive to the base paired with a lesion

The human alkyladenine DNA glycosylase has a broad substrate specificity, excising a structurally diverse group of damaged purines from DNA. To more clearly define the structural and mechanistic bases for substrate specificity of human alkyladenine DNA glycosylase, kinetics of excision and DNA binding activities were measured for several different damaged and undamaged purines within identical DNA sequence contexts. We found that 1,N(6)-ethenoadenine (epsilonA) and hypoxanthine (Hx) were excised relatively efficiently, whereas 7,8-dihydro-8-oxoguanine, O(6)-methylguanine, adenine, and guanine were not. Single-turnover kinetics of excision of Hx and epsilonA paired with T showed that excision of Hx was about four times faster than epsilonA, whereas binding assays showed that the binding affinity was about five times greater for epsilonA than for Hx. The opposing pyrimidine base had a significant effect on the kinetics of excision and DNA binding affinity of Hx but a small effect on those for epsilonA. Surprisingly, replacing a T with a U opposite Hx dramatically reduced the excision rate by a factor of 15 and increased the affinity by a factor of 7-8. The binding affinity of human alkyladenine DNA glycosylase to a DNA product containing an abasic site was similar to that for an Hx lesion.

Molecular basis for discriminating between normal and damaged bases by the human alkyladenine glycosylase, AAG

The human 3-methyladenine DNA glycosylase [alkyladenine DNA glycosylase (AAG)] catalyzes the first step of base excision repair by cleaving damaged bases from DNA. Unlike other DNA glycosylases that are specific for a particular type of damaged base, AAG excises a chemically diverse selection of substrate bases damaged by alkylation or deamination. The 2.1-A crystal structure of AAG complexed to DNA containing 1,N(6)-ethenoadenine suggests how modified bases can be distinguished from normal DNA bases in the enzyme active site. Mutational analyses of residues contacting the alkylated base in the crystal structures suggest that the shape of the damaged base, its hydrogen-bonding characteristics, and its aromaticity all contribute to the selective recognition of damage by AAG.

3-methyladenine DNA glycosylases: structure, function, and biological importance

The genome continuously suffers damage due to its reactivity with chemical and physical agents. Finding such damage in genomes (that can be several million to several billion nucleotide base pairs in size) is a seemingly daunting task. 3-Methyladenine DNA glycosylases can initiate the base excision repair (BER) of an extraordinarily wide range of substrate bases. The advantage of such broad substrate recognition is that these enzymes provide resistance to a wide variety of DNA damaging agents; however, under certain circumstances, the eclectic nature of these enzymes can confer some biological disadvantages. Solving the X-ray crystal structures of two 3-methyladenine DNA glycosylases, and creating cells and animals altered for this activity, contributes to our understanding of their enzyme mechanism and how such enzymes influence the biological response of organisms to several different types of DNA damage.

3-methyladenine DNA glycosylases: structure, function, and biological importance

The genome continuously suffers damage due to its reactivity with chemical and physical agents. Finding such damage in genomes (that can be several million to several billion nucleotide base pairs in size) is a seemingly daunting task. 3-Methyladenine DNA glycosylases can initiate the base excision repair (BER) of an extraordinarily wide range of substrate bases. The advantage of such broad substrate recognition is that these enzymes provide resistance to a wide variety of DNA damaging agents; however, under certain circumstances, the eclectic nature of these enzymes can confer some biological disadvantages. Solving the X-ray crystal structures of two 3-methyladenine DNA glycosylases, and creating cells and animals altered for this activity, contributes to our understanding of their enzyme mechanism and how such enzymes influence the biological response of organisms to several different types of DNA damage.

Crystal structure of a human alkylbase-DNA repair enzyme complexed to DNA: mechanisms for nucleotide flipping and base excision

DNA N-glycosylases are base excision-repair proteins that locate and cleave damaged bases from DNA as the first step in restoring the genetic blueprint. The human enzyme 3-methyladenine DNA glycosylase removes a diverse group of damaged bases from DNA, including cytotoxic and mutagenic alkylation adducts of purines. We report the crystal structure of human 3-methyladenine DNA glycosylase complexed to a mechanism-based pyrrolidine inhibitor. The enzyme has intercalated into the minor groove of DNA, causing the abasic pyrrolidine nucleotide to flip into the enzyme active site, where a bound water is poised for nucleophilic attack. The structure shows an elegant means of exposing a nucleotide for base excision as well as a network of residues that could catalyze the in-line displacement of a damaged base from the phosphodeoxyribose backbone.

Studying How Different Terminal Groups Change the Motion of H2NSO2C6H4CONH(EG)3R When Bound to the Active Site of Human Carbonic Anhydrase II

Molecular dynamics simulations have been used to explore the motions of series of ligands containing coupled benzenesulfonamide and oligoethylene glycol moieties (H2NSO2C6H4CONH(CH2-CH2OCH2CH2OCH2CH2)R+; R+ = NH3+, NHCOCH2NH3+, NHCOCH(CH2Ph)NH3+) bound at the active site of human carbonic anhydrase II (HCAII; E.C. 4.2.1.1). These complexes have been examined previously by X-ray crystallography; the locations of the terminal groups of these ligands were not defined in the crystal structures. These stimulations, carried out in the presence of water, provide dynamic information about the motion of the bound ligand that supplements the quasistatic information from crystallography. Our results suggested that the Gly and Phe groups of these ligands interacted weakly with the protein adjacent to the active site. Quantitative estimates of energies of binding did not correlate usefully with observed free energies of binding, but in the absence of information about entropies, it is not possible to tell if the lack of correlation between calculated energies and observed free energies represents inaccuracies in the energies, or a compensation between enthalpies and entropies. When the terminal Phe group was placed near a previously identified hydrophobic patch in the active site (Phe20 and Pro202) the average conformation of the ligand inferred from this simulation was inconsistent with that from the crystal structure; this result illustrates the problems of misleading local minima in these types of simulations.

Comparison of a new, rapid enzyme immunoassay with a latex agglutination test for qualitative detection of rubella antibodies

A total of 450 sera were tested for rubella virus antibodies by using a new, rapid enzyme immunoassay, SUDS Rubella. The results were compared with those obtained by using the Rubascan test, a well-established latex agglutination method. The sensitivity of the SUDS Rubella was 99.5%, and the specificity was 100%, when compared with Rubascan. The SUDS Rubella test can be performed in 10 min and provides an accurate screening test for the detection of rubella antibodies.