Studies on hyperthermostable aldolase : characteristics, structure and application

点击翻译按钮获取中文摘要

A gene encoding a D-2-deoxyribose-5-phosphate aldolase (DERA) homologue was identified in the hyperthermophilic archaeon Aeropyrum pernix. The gene was overexpressed in Escherichia coli, and the produced enzyme was purified and characterized. The enzyme was an extremely thermostable DERA ; the activity was not lost after incubation at 100℃ for 10 min. The enzyme had a molecular mass of about 93 kDa and consisted of four subunits with an identical molecular mass of 24 kDa. This shows the first presence of the tetrameric DERA. The three-dimensional structure of the enzyme was determined by x-ray analysis. The subunit folded into an α/β barrel. The asymmetric unit consisted of two homologous subunits, and a crystallographic 2-fold axis generated the functional tetramer. Compared with the structure of the E. coli DERA, the mainchain coordinate of the monomer of A. pernix enzyme was quite similar to that of the E. coli enzyme. A large difference in hydrophobic interactions and the number of ion pairs was not observed between the monomeric structures of the two enzymes. However, a significant difference in the quaternary structure was observed. The area of the subunit-subunit interface in the dimer of the A. pernix enzyme was much larger than the corresponding one of the E. coli enzyme. In addition, the A. pernix enzyme was 10 amino acids longer than the E. coli enzyme in the N-terminal region and exhibited an additional N-terminal helix. The N-terminal helix produced a unique dimer-dimer interface. This promotes the formation of a functional tetramer of the A. pernix enzyme and strengthens the hydrophobic inter-subunit interactions. These structural features are considered to be responsible for the extremely high stability of the A. pernix enzyme. This is the first description of the structure of hyperthermophilic DERA and of aldolase from the domain of archaea.