Peptidyl-Lys metalloendopeptidase

This chapter discusses the structural chemistry and the biological aspects of peptidyl-lys metalloendopeptidase. The name peptidyl-lys metalloendopeptidase is based on the substrate specificity (Xaa–Lys) of the enzyme. The reported isoelectric points are pH 7.5 (GfMEP) and 8.4 (PoMEP). These enzymes contain one zinc atom per molecule (AmMEP, GfMEP and PoMEP) as an essential component. Two enzymes, MyMEP and AmMEP, are reported to be composed of 157 and 154 amino acids with minimum molecular masses of 16,600 and 16,650 Da, respectively. Primary structures of the two mushroom enzymes have been determined and nucleotide sequences of precursor proteins of AmMEP, GfMEP and AhMEP have been deposited in databases. They are the homologous proteins of 167 (GfMEP) and 168 (PoMEP and AmMEP) amino acid residues with 42.3–61.3% identity, and molecular masses are calculated to be about 18,000. The enzymes are found exclusively in fruiting bodies of higher basidiomycetes, except for MyMEP. Although My MEP is secreted into culture media, possibly to extract nutrients from extracellular proteins, the function of the mushroom enzymes internally is not clear.