| Type: | Family | Name: | Serine endopeptidase DegP2 |
| Description: | The DegP/Htr family in Prokaryota, including cyanobacteria from which chloroplasts derive, consists of three serine-type endopeptidases: DegP (also named HtrA), DegQ (also named HhoA) and DegS (also named HtrH or HhoB). Consistent with the prokaryotic origins of chloroplasts a Arabidopsis thaliana(Mouse-ear cress) DegP2 gene encoding a novel chloroplast homologue of the prokaryotic trypsin-type Deg/Htr serine proteases has been identified.DegP is essential for bacterial survival at temperatures above 42 degrees and for digesting misfolded protein in the periplasm. Mature DegP from Escherichia colihas 448 residues, of which His105, Asp135, and Ser210 form the catalytic triad. The protein has an N-terminal sequence typical of a leader peptide. Structural analysis indicates that bacterial HtrA is a serine protease belonging to the family of cage-forming proteases and only unfolded polypeptides can be threaded in extended conformation into the cage to access the proteolytic sites. Disulphide bonds of partially unfolded substrates impede protein breakdown and represent a conformational constraint for entering the inner cavity. This preference for unfolded polypeptides might be the reason for the increased proteolytic activity at higher temperatures.The DegP/Htr family shares a modular architecture composed of an N-terminal segment believed to have regulatory functions, a conserved trypsin-like protease domain, and one or two PDZ domains, which mediate specific protein-protein interactions and bind preferentially to the C-terminal three to four residues of the target protein. DegP belongs to the trypsin clan SA. SA-type proteases have a two-domain structure with each domain forming a six-stranded barrel. The active site cleft is located at the interface of the two perpendicularly arranged barrel domains. The active site is constructed by several loops located at the C-terminal side of both barrel domains. The functional unit of DegP appears to be a trimer, which is stabilised exclusively by residues of the protease domains. The basic trimer has a funnel-like shape with the protease domains located at its top and the PDZ domains protruding to the outside. Once substrates have been bound, they have to be delivered into the interior of the funnel and the proteolytic sites. In contrast to other protease-chaperone systems, ATP does not drive binding and release of substrates.The degQ and degS genes of E. coli encode proteins of 455 and 355 residues that are homologues of the DegP protease. Purified DegQ protein has the properties of a serine endopeptidase, and is processed by the removal of a 27-residue N-terminal signal sequence. Deletion studies suggest that DegQ, like DegP, functions as a periplasmic protease in vivo.This entry represents a set of known and suspected serine proteases related to DegP2 from Arabidopsis thaliana. DegP2 is a serine protease that performs the primary cleavage of the photodamaged D1 protein in plant photosystem II []. | Short Name: | Pept_DepP2 |
