RecA stimulates AlkB-mediated direct repair of DNA adducts.

The Escherichia coli AlkB protein is a 2-oxoglutarate/Fe(II)-dependent demethylase that repairs alkylated single stranded and double stranded DNA. Immunoaffinity chromatography coupled with mass spectrometry identified RecA, a key factor in homologous recombination, as an AlkB-associated protein. The interaction between AlkB and RecA was validated by yeast two-hybrid assay; size-exclusion chromatography and standard pull down experiment and was shown to be direct and mediated by the N-terminal domain of RecA. RecA binding results AlkB-RecA heterodimer formation and RecA-AlkB repairs alkylated DNA with higher efficiency than AlkB alone.

2-Hydrazinobenzothiazole-based etheno-adduct repair protocol (HERP): a method for quantitative determination of direct repair of etheno-bases.

Etheno-DNA adducts are mutagenic and lead to genomic instability. Enzymes belonging to Fe(II)/2-oxoglutarate-dependent dioxygenase family repair etheno-DNA adducts by directly removing alkyl chain as glyoxal. Presently there is no simple method to assess repair reaction of etheno-adducts. We have developed a rapid and sensitive assay for studying etheno-DNA adduct repair by Fe(II)/2-oxoglutarate-dependent dioxygenases. Using AlkB as model Fe(II)/2-oxoglutarate-dependent dioxygenases, we performed in vitro repair of etheno-adducts containing DNA and detected glyoxal by reacting with 2-hydrazinobenzothiazole which forms complex yellow color compound with distinct absorption spectrum with a peak absorption at 365 nm. We refer this method as 2-hydrazinobenzothiazole-based etheno-adduct repair protocol or HERP. Our novel approach for determining repair of etheno-adducts containing DNA overcomes several drawbacks of currently available radioisotope-based assay.

Citrate-capped gold nanoparticles for the label-free detection of ubiquitin C-terminal hydrolase-1.

Ubiquitin C-terminal hydrolase-1 (UCH-L1) is a specific neuronal endoprotease that cleaves the specific peptide bond between ubiquitin molecules. UCH-L1 is released in serum and cerebrospinal fluid after severe brain injury and is considered to be an important biomarker of brain injury. A common polymorphism of UCH-L1 (S18Y) is also linked to a reduced risk of Parkinson's disease. In addition to its function in neuronal tissues, UCH-L1 may also play a part in the progression of certain non-neuronal cancers. UCH-L1 is highly expressed in primary lung tumors and colo-rectal cancers, suggesting a role in tumorigenesis. We report here the development of a sensitive and accurate UCH-L1 assay based on the surface plasmon resonance (SPR) absorbance of gold nanoparticles. We created a unique UCH-L1 substrate containing a ubiquitin molecule with two terminal thiol groups. This UCH-L1 substrate interacted with gold nanoparticles via the terminal thiol groups and induced clustering of the nanoparticles, which was detected by SPR absorbance at 650 nm. UCH-L1 proteolytically cleaved the substrate and the clustered gold nanoparticles were dispersed and could be detected by a shift in the SPR absorbance to 530 nm. This change in absorbance was proportional to the concentration of UCH-L1 and can be used for the quantification of functional UCH-L1. The currently available fluorescence-based UCH-L1 assay is affected by a high background signal and a poor detection limit, especially in the presence of serum. The assay reported here can detect concentrations of UCH-L1 as low as 20 ng ml(-1) (0.8 nM) and the presence of serum had no effect on the detection limit. This assay could be adapted for the rapid determination of the severity of brain injury and could also be applied to high-throughput screening of inhibitors of UCH-L1 enzymatic activity in Parkinson's disease and cancer.

A role for Saccharomyces cerevisiae Tpa1 protein in direct alkylation repair.

Alkylating agents induce cytotoxic DNA base adducts. In this work, we provide evidence to suggest, for the first time, that Saccharomyces cerevisiae Tpa1 protein is involved in DNA alkylation repair. Little is known about Tpa1 as a repair protein beyond the initial observation from a high-throughput analysis indicating that deletion of TPA1 causes methyl methane sulfonate sensitivity in S. cerevisiae. Using purified Tpa1, we demonstrate that Tpa1 repairs both single- and double-stranded methylated DNA. Tpa1 is a member of the Fe(II) and 2-oxoglutarate-dependent dioxygenase family, and we show that mutation of the amino acid residues involved in cofactor binding abolishes the Tpa1 DNA repair activity. Deletion of TPA1 along with the base excision repair pathway DNA glycosylase MAG1 renders the tpa1Δmag1Δ double mutant highly susceptible to methylation-induced toxicity. We further demonstrate that the trans-lesion synthesis DNA polymerase Polζ (REV3) plays a key role in tolerating DNA methyl-base lesions and that tpa1Δmag1revΔ3 triple mutant is extremely susceptible to methylation-induced toxicity. Our results indicate a synergism between the base excision repair pathway and direct alkylation repair by Tpa1 in S. cerevisiae. We conclude that Tpa1 is a hitherto unidentified DNA repair protein in yeast and that it plays a crucial role in reverting alkylated DNA base lesions and cytotoxicity.

A nonradioactive restriction enzyme-mediated assay to detect DNA repair by Fe(II)/2-oxoglutarate-dependent dioxygenase.

The Escherichia coli DNA repair enzyme AlkB belongs to the Fe(II)/2-oxoglutarate-dependent dioxygenase family. It removes methyl groups from 1-methyl adenine (1-meA) and 3-methyl cytosine (3-meC) lesions present in single-stranded DNA by oxidative decarboxylation. In the current article, we describe an in vitro assay that permits rapid detection of AlkB activity. To achieve this, we generated methylated oligonucleotide using methyl methanesulfonate and then monitored DNA repair using a methylation-sensitive restriction enzyme and novel agarose gel electrophoresis system capable of resolving small oligonucleotides. Our approach overcomes several drawbacks of NAD(+)-dependent formaldehyde dehydrogenase-coupled assay and radioisotope-based assay for determining AlkB DNA repair activity.

Syntheses of a library of molecules on the marine natural product ianthelliformisamines platform and their biological evaluation.

Ianthelliformisamines A-C are a novel class of bromotyrosine-derived antibacterial agents isolated recently from the marine sponge Suberea ianthelliformis. We have synthesized ianthelliformisamines A-C straightforwardly by the condensation of (E)-3-(3,5-dibromo-4-methoxyphenyl)acrylic acid and the corresponding Boc-protected polyamine followed by Boc-deprotection with TFA. Further, using this reaction protocol, a library of their analogues (39 analogues) has been synthesized by employing 3-phenylacrylic acid derivatives and Boc-protected polyamine chains through various combinations of these two fragments differing in phenyl ring substitution, double bond geometry or chain length of the central spacer of the polyamine chain (shown in red color). All the synthesized compounds (ianthelliformisamines A-C and their analogues) were screened for antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) strains. All synthetic analogues of ianthelliformisamine A showed bacterial growth inhibition against both strains (Escherichia coli and Staphylococcus aureus), having MIC values in the range of 117.8-0.10 µM, while none of the synthetic analogues of ianthelliformisamine C as well as the parent compound showed any detectable antibacterial activity. Interestingly, some of the synthetic analogues of ianthelliformisamines A and B exerted a bactericidal effect against both E. coli and S. aureus strains, decreasing viable bacterial count by 99% at concentrations as low as 2 × MIC.