Glutamic proteases are a group of proteolyticenzymes containing a glutamic acid residue within the active site. This type of protease was first described in 2004 and became the sixth catalytic type of protease.[1] Members of this group of protease had been previously assumed to be an aspartate protease, but structural determination showed it to belong to a novel protease family. The first structure of this group of protease was scytalidoglutamic peptidase, the active site of which contains a catalytic dyad, glutamic acid (E) and glutamine (Q), which give rise to the name eqolisin. This group of proteases are found primarily in pathogenic fungi affecting plant and human.[2]
There are two independent families of glutamic proteases (G1 and G2), and have a limited distribution. They were originally thought to be limited to filamentous fungi mainly in the Ascomycota phylum.[3] Subsequently, however, glutamic proteases have been identified in bacteria and archaea.[4] A glutamic protease from a plant virus (strawberry mottle virus) has also been identified.[5]
A convergently evolved glutamic peptidase, the pre-neck appendage protein (bacteriophage phi-29), uses a Glu and Asp dyad at the active site, and is classified as MEROPS family G2.[8]
These enzymes are acid proteases; eqolisin for example is most active at pH 2.0 when casein is used as substrate.[2] Eqolosins prefer bulky amino acid residues at the P1 site and small amino acid residues at the P1′ site.
A characteristic of the protease is its insensitivity to pepstatin and S-PI (acetyl pepstatin) and it was previously classed as "pepstatin-insensitive carboxyl proteinases".[9] The other "pepstatin-insensitive carboxyl proteinases" belongs to subfamily of serine protease, serine-carboxyl protease (sedolisin) which was discovered in 2001.[2] These proteases are also not inhibited by DAN (diazoacetyl-DL-norleucine methylester) (7) but may be inhibited by EPNP (1,2-epoxy-3-(p-nitrophenoxy) propane).[10][11]
The active site of eqolosin contains a distinctive glutamic acid and glutamine catalytic dyad which are involved in substrate binding and catalysis. These residues act as a nucleophile, with the glutamic acid serving as a general acid in the first phase of the reaction, donating a proton to the carbonyl oxygen in the peptide bond of the substrate. One or two water molecules may be involved in the reaction supplying a hydroxyl group, and the glutamic acid further donates a proton to the amide nitrogen, resulting in breakage of the peptide bond. The glutamine then returns the glutamic acid to its initial state.[12]
^Sasaki H, Kubota K, Lee WC, Ohtsuka J, Kojima M, Iwata S, Nakagawa A, Takahashi K, Tanokura M (Jul 2012). "The crystal structure of an intermediate dimer of aspergilloglutamic peptidase that mimics the enzyme-activation product complex produced upon autoproteolysis". Journal of Biochemistry. 152 (1): 45–52. doi:10.1093/jb/mvs050. PMID22569035.
