Spherulation-specific family 4. This protein is found in bacteria, archaea and eukaryotes. Proteins in this family are typically between 250 and 398 amino acids in length. There is a conserved NPG sequence motif and there are two completely conserved G residues that may be functionally important. Starvation will often induce spherulation - the production of spores - and this process may involve DNA-methylation. Changes in the methylation of spherulin4 are associated with the formation of spherules, but these changes are probably transient. Methylation of the gene accompanies its transcriptional activation, and spherulin4 mRNA is only detectable in late spherulating cultures and mature spherules. It is a spherulation-specific protein.
Peptidase M35 domain of deuterolysins and related proteins. This family M35 Zn2+-metallopeptidase extracellular domain is found in fungal deutrolysins (acid metalloproteinase, neutral proteinase II), including some well-characterized metallopeptidase domains in Aspergillus oryzae (NpII), Aspergillus fumigatus (MEP20), Penicillium roqueforti (protease II) and Emericella nidulans (PepJ peptidase). The neutral proteinase II from Aspergillus oryzae (NpII) unfolds reversibly upon incubation at higher temperatures, and loss in activity is mainly due to autoproteolysis. MEP20 is encoded by the mepB gene, which appears to be associated with the cytoplasmic degradation of small peptides. PepJ peptidase is a thermostable enzyme released under carbon starvation. Most members of this family contain a unique zinc-binding motif (the aspzincin motif), defined by the HExxH + D motif where an aspartic acid is the third zinc ligand and is found in a GTXDXXYG or similar motif C-terminal to the His zinc ligands. The aspzincin motif is poorly conserved in one subgroup, that includes Asp f2, a major allergen from Aspergillus fumigatus. This subgroup in addition lacks the key conserved Tyr residue which acts as a proton donor during catalysis, and no protease activity has been detected to date for Asp f2.
