Structure of the type I L-asparaginase from the hyperthermophilic archaeon Pyrococcus horikoshii at 2.16 angstroms resolution.Yao, M., Yasutake, Y., Morita, H., Tanaka, I.
(2005) Acta Crystallogr D Biol Crystallogr 61: 294-301
- PubMed: 15735339
- DOI: https://doi.org/10.1107/S0907444904032950
- Primary Citation of Related Structures:
- PubMed Abstract:
The crystal structure of the L-asparaginase from the hyperthermophilic archaeon Pyrococcus horikoshii (PhA) was determined by the multiwavelength anomalous diffraction (MAD) method and was refined to a resolution of 2.16 angstroms with a crystallographic R factor and free R factor of 21.1 and 25.3%, respectively. This is the first report of the three-dimensional structure of a type I L-asparaginase. These enyzmes are known as cytosolic L-asparaginases with lower affinities for substrate than the type II L-asparaginases. Although the overall fold of PhA was closely related to the structure of the well characterized type II L-asparaginase, structural differences were also detected. PhA forms a homodimer that corresponds to half the homotetramer of type II L-asparaginases. Structure comparison at the active site reveals that most catalytic residues are conserved except for two residues that recognize the amino group of the substrate. Additionally, a remarkable structural difference is found in the so-called 'active-site flexible loop'. In PhA this loop is stabilized by beta-hairpin formation and by elaborate interactions with the type-I-specific alpha-helical region derived from the other subunit forming the PhA dimer. The flexible loop of the type II enzyme is considered to serve as a mobile gate to the active site. Therefore, the loop stabilization observed in the PhA structure may cause limitation of the access of the substrate to the active site.
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Kita-10, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan.