Adenylate kinase from chlamydia pneumoniae

Chlamydiae proliferate only within the infected host cells and are thought to be ”energy parasites,” because they take up ATP from the host cell as an energy source. We isolated from Chlamydia pneumoniae the gene encoding adenylate kinase (AK) that contributes to the homeostasis of the intracellular adenine nucleotide pool in many organisms. K_m values for AMP and for ADP of the purified C. pneumoniae AK (AKcpn) were significantly higher than the reported values of other AKs, suggesting correlation with high concentration of chlamydial intracellular AMP. According to these findings, a new model of ATP import mechanism by Chlamydia was proposed. AKcpn contains 1 g atom of zinc per mole of 24,000-dalton protein. Mass spectrometric analysis of AKcpn and analysis of properties of mutated AKcpn strongly suggested that zinc is associated with four cysteine residues in the LID domain of the enzyme. Although the apo-AKcpn that lost zinc retained AK activity, it was more thermolabile and sensitive to trypsin digestion than the holo-AKcpn, indicating that the zinc in AKcpn contributes to thermal stability of the protein. Moreover, the recovery in vitro of the AK activity during the renaturation process of the denatured apo-AKcpn was dependent on zinc. These results indicate that zinc in AKcpn, although not essential for the catalysis, stabilizes the enzyme and probably plays a crucial role in proper folding of the protein.

肺炎クラミジア

アデニル酸キナーゼ

亜鉛結合タンパク質

プロテインフォールディング

本文データは山口大学医学会の許諾に基づきCiNiiから複製したものである