Structural aspects of L-asparaginases, their friends and relations.
Enzymes capable of converting L-asparagine to L-aspartate can be classified as bacterial-type or plant-type L-asparaginases. Bacterial-type L-asparaginases are further divided into subtypes I and II, defined by their intra-/extra-cellular localization, substrate affinity, and oligomeric form. Plant-type L-asparaginases are evolutionarily and structurally distinct from the bacterial-type enzymes. They function as potassium-dependent or -independent Ntn-hydrolases, similar to the well characterized aspartylglucosaminidases with (alphabeta)2 oligomeric structure. The review discusses the structural aspects of both types of L-asparaginases and highlights some peculiarities of their catalytic mechanisms. The bacterial-type enzymes are believed to have a disordered active site which gets properly organized on substrate binding. The plant-type enzymes, which are more active as isoaspartyl aminopeptidases, pose a chemical challenge common to other Ntn-hydrolases, which is how an N-terminal nucleophile can activate itself or cleave its own alpha-amide bond before the activation is even possible. The K+ -independent plant-type L-asparaginases show an unusual sodium coordination by main-chain carbonyl groups and have a key arginine residue which by sensing the arrangement at the oligomeric (alphabeta)-(alphabeta) interface is able to discriminate among substrates presented for hydrolysis.
Michalska
Karolina
K
Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznań, Poland.
Jaskolski
Mariusz
M
D001215:Asparaginase / Q000737:chemistry* / Q000145:classification; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification; D002384:Catalysis; D010940:Plant Proteins / Q000737:chemistry / Q000145:classification; D011487:Protein Conformation; D013379:Substrate Specificity
D001426:Bacterial Proteins; D010940:Plant Proteins; D001215:Asparaginase