Abnormal junctional membrane structures in cardiac myocytes expressing ectopic junctophilin type 1

A gene encoding a putative ATP-dependent DNA ligase from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1 was cloned and the biochemical characteristics of the resulting recombinant protein were examined. The gene (accession no. APE1094) from A. pernix encoding a 69-kDa protein showed a 39–61% identity with other ATP-dependent DNA ligases from the archaea. Normally DNA ligase is activated by NAD⁺ or ATP. There has been no report about the other activators for DNA ligase. The recombinant ligase was a monomeric protein and catalyzed strand joining on a singly nicked DNA substrate in the presence of ADP and a divalent cation (Mg²⁺, Mn²⁺, Ca²⁺ and Co²⁺) at high temperature. The optimum temperature and pH for nick-closing activity were above 70°C and 7.5°C, respectively. The ligase remained stable for 60 min of treatment at 100°C, and the half-life was about 25 min at 110°C. This is the first report of a novel hyperthermostable DNA ligase that can utilize ADP to activate the enzyme.