Novel non-isotopic detection of MutY enzyme-recognized mismatches in DNA via ultrasensitive detection of aldehydes.

A highly sensitive method to detect traces of aldehyde-containing apurinic/apyrimidinic (AP) sites in nucleic acids has been developed. Based on this method, a novel approach to detect DNA base mismatches recognized by the mismatch repair glycosylase MutY is demonstrated. Open chain aldehydes generated in nucleic acids due to spontaneous depurination, DNA damage or base excision of mismatched adenine by MutY are covalently trapped by a new linker molecule [fluorescent aldehyde-reactive probe (FARP), a fluorescein-conjugated hydroxylamine derivative]. DNA containing AP sites is FARP-trapped, biotinylated and immobilized onto neutravidin-coated microplates. The number of FARP-trapped aldehydes is then determined via chemiluminescence using a cooled ICCD camera. AP sites induced in plasmid or genomic calf thymus DNA via mild depurination or by simple incubation at physiological conditions (pH 7, 37 degreesC) presented a linear increase in chemiluminescence signal with time. The procedure developed, from a starting DNA material of approximately 100 ng, allows detection of attomole level (10(-18) mol) AP sites, or 1 AP site/2 x 10(7) bases, and extends by 1-2 orders of magnitude the current limit in AP site detection. In order to detect MutY-recognized mismatches, nucleic acids are first treated with 5 mM hydroxylamine to remove traces of spontaneous aldehydes. Following MutY treatment and FARP-labeling, oligonucleotides engineered to have a centrally located A/G mismatch demonstrate a strong chemiluminescence signal. Similarly, single-stranded M13 DNA that forms mismatches via self-complementation (average of 3 mismatches over 7429 bases) and treated with MutY yields a signal approximately 100-fold above background. No signal was detected when DNA without mismatches was used. The current development allows sensitive, non-isotopic, high throughput screening of diverse nucleic acids for AP sites and mismatches in a microplate-based format.