First characterisation of a CPD-class I photolyase from a UV-resistant extremophile isolated from High-Altitude Andean Lakes.

UV-resistant Acinetobacter sp. Ver3 isolated from High-Altitude Andean Lakes (HAAL) in Argentinean Puna, one of the highest UV exposed ecosystems on Earth, showed efficient DNA photorepairing ability, coupled to highly efficient antioxidant enzyme activities in response to UV-B stress. We herein present the cloning, expression, and functional characterization of a cyclobutane pyrimidine dimer (CPD)-class I photolyase (Ver3Phr) from this extremophile to prove its involvement in the previously noted survival capability. Spectroscopy of the overexpressed and purified protein identified flavin adenine dinucleotide (FAD) and 5,10-methenyltetrahydrofolate (MTHF) as chromophore and antenna molecules, respectively. All functional analyses were performed in parallel with the ortholog E. coli photolyase. Whereas the E. coli enzyme showed the FAD chromophore as a mixture of oxidised and reduced states, the Ver3 chromophore always remained partly (including the semiquinone state) or fully reduced under all experimental conditions tested. Functional complementation of Ver3Phr in Phr(-)-RecA E. coli strains was assessed by traditional UFC counting and measurement of DNA bipyrimidine photoproducts by HPLC coupled with electrospray ionisation-tandem mass spectrometry (ESI-MS/MS) detection. The results identified strong photoreactivation ability in vivo of Ver3Phr while its nonphotoreactivation function, probably related with the stimulation of nucleotide excision repair (NER), was not as manifest as for EcPhr. Whether this is a question of the approach using an exogenous photolyase incorporated in a non-genuine host or a fundamental different behaviour of a novel enzyme from an exotic environment will need further studies.