Class 2 L-asparaginases, previously known as plant-type L-asparaginases, are the second largest class. In the majority of cases the L-asparaginase activity is secondary: these enzymes preferably catalyse other reactions. However, Class 2 enzymes also consistently display L-asparaginase activity. It should be noted that this does not mean the L-asparaginase activity is biologically unimportant or that there could not a Class 2 L-asparaginase with L-asparagine as the primary substrate.
Class 2 L-asparaginases can be found in bacteria, archaea, and eukaryotes, including humans. They have various names as they catalyse different reactions: aspartylglucosaminidase, often incorrectly glycosylasparaginase, threonine aspartase, isoaspartyl peptidase and/or L-asparaginase, however, the Km for L-asparagine is generally high throughout the class.
This class of L-asparaginases is similarly well conserved structurally, even though the shared sequence identity can be low. In most cases they are first transcribed as ~35 kDa precursors which create inactive dimers that are autocatalytically cleaved into an N-terminal α (~20 kDa) and a C-terminal β subunit (~15 kDa), which assemble to create the mature protein. One could view the structure as a dimer of two αβ hetero dimers or as a hetero tetramer.
