Table 2.

Most studied microbial endopeptidases cleaving proline- and glutamine-rich prolamine molecules

Enzyme family	Cleavage site	Substrate	Subcellular location	pH optimum	Temp. optimum (°C)	Microbe; peptidase	Origin	Reference
Metallopeptidase
M4 elastase	Q↓L	Intact molecule	Extracellular	2.0–7.0	37	Bacteria; Pseudomonas aeruginosa; LasB	Human feces	(Wei et al. 2015; Caminero et al. 2016)
Serine peptidase
S8 subtilisin	XPQ↓; LPY↓	Intact molecule	Extracellular	3–10	37	Bacteria; Rothia spp.	Human oral cavity	(Zamakhchari et al. 2011)
S9A prolyl-oligopeptidase	P↓F; P↓Y; P↓Q	Oligopeptide	Cytosolic	6.0–7.0	37	Bacteria; Myxococcus xanthus	Soil	(Shan et al. 2004; Kocadag Kocazorbaz and Zihnioglu 2017)
	P↓Q; P↓Y	Oligopeptide	Periplasmic	6.0–7.0	43	Bacteria; Sphingomonas capsulata	Distilled water	(Kabashima et al. 1998; Shan et al. 2004)
	GP↓; AP↓	Oligopeptide	Extracellular	6.0–8.0		Bacteria; Chryseobacterium taeanense	Rhizosphere of cereal crops	(de Amador et al. 2019)
	SAP↓; GGP↓; TP↓G; GP↓	ND	Cytosolic	6.0–9.0	37	Bacteria; Cellulomonas sp.	Human gut	(Kumar et al. 2018)
	P↓Q; P↓F; P↓Y	Oligopeptide	Cytosolic	5.0–8.0	63	Bacteria; Sphaerobacter thermophilus	Sewage sludge	(Pati et al. 2010; Shetty et al. 2017)
	GP↓; AP↓: AA↓	Intact molecule, oligopeptide	Not exported	∼7	85–90	Archaea; Pyrococcus furiosus		(Harwood et al. 1997; Harris et al. 2001)
S28 prolyl endopeptidase	XP↓	Intact molecule, oligopeptide	Extracellular	4.0–5.0	15–60	Fungi; Aspergillus niger		(Edens et al. 2005)
S53 serine-carboxyl peptidase	F↓P; Q↓L	Intact molecule	Extracellular	3.0–6.0	37	Bacteria; Actinoallomurus A8	Soil pH 4.2	(Cavaletti et al. 2019)