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Query: UNIPROT:P04040 (Catalase)
 3,577 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Catalase is a ubiquitous peroxisomal matrix enzyme, yet the molecular targeting signal(s) for sorting it in plant cells has not been defined. The most common peroxisome targeting signal (PTS) is a C-terminal tripeptide composed of a conserved SKL motif (type 1 PTS). The PTS for cottonseed catalase (Ccat) was elucidated in this study from immunofluorescence microscopic analyses of tobacco BY-2 suspension cells serving as an in vivo import system. To distinguish biolistically introduced Ccat from endogenous tobacco catalase, Ccat was hemagglutinin (HA)epitope-tagged at its N-terminus. Bombardment with HA-Ccat resulted in the import of Ccat into glyoxysomes, the specialized type of peroxisome in BY-2 cells. The C-terminal tripeptide of Ccat, PSI, is necessary for import. Evidence for this were mislocalizations to the cytosol of PSI-truncated Ccat and AGV-substituted (for PSI) Ccat. PSI-COOH, however, was not sufficient to re-route chloramphenicol acetyltransferase (CAT) from the cytosol to glyoxysomes, whereas the Ccat tetrapeptide RPSI-COOH was sufficient. Surprisingly, substitution of K (common at the fourth position in other plant catalases) for the R (CAT-KPSI) decreased import efficiency. However, substitution of K did not affect import, when additional upstream residues in Ccat were included (e.g. CAT-NVKPSI). Other evidence for the importance of upstream residues comprised abolishment of Ccat import due to substitutions with non-conserved residues (e.g. -AGVNVRPSI for -SRLNVRPSI). These data indicate that Ccat is sorted to plant peroxisomes by a degenerate type 1 PTS (PSI-COOH) whose residues are functionally dependent on a strict context of adjacent C-terminal amino acid residues.
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PMID:Identification of the peroxisomal targeting signal for cottonseed catalase. 930 Oct 84

The majority of proteins targeted to the peroxisomal lumen contain a C-terminal peroxisomal targeting signal-1 (PTS1) that is bound by the peroxin Pex5p. The PTS1 is generally regarded as a C-terminal tripeptide that adheres to the consensus (S/A/C)(K/R/H)(L/M). Previously, we studied the binding affinity of peptides of the form YQX(-3)X(-2)X(-1) to the peptide-binding domain of human Pex5p (referred to as Pex5p-C). Optimal affinity was found for YQSKL, which bound with an affinity of 200 +/- 40 nM. To extend this work, we investigated the properties of a peptide containing the last 9 residues of acyl-CoA oxidase (RHYLKPLQSKL) and discovered that it binds to Pex5p-C with a dissociation constant of 1.4 +/- 0.4 nM, 180 times tighter than YQSKL. Further analysis revealed that the enhanced affinity is primarily due to the presence of leucine in the (-5) position. In addition, a peptide corresponding to the luciferase C-terminus (YKGGKSKL) was found to bind Pex5p-C about 20 times tighter than YQSKL. The majority of this effect results from having lysine in position (-4). Catalase contains a noncanonical PTS1 (-AREKANL). The affinity of YQANL was found to be 3600 +/- 400 nM. This relatively weak binding is consistent with previous unsuccessful attempts to direct chloramphenicol acetyltransferase to the peroxisome by fusing -ANL to its C-terminus (-GGA-ANL). The peptides YKANL, YEKANL, YREKANL, and YAREKANL all bound Pex5p-C with higher affinities than did YQANL, but the affinities are still lower than peptides that correspond to functional targeting signals in other contexts. Because both catalase and Pex5p are tetramers (as opposed to the monomeric Pex5p-C and the peptides used in our studies), multidentate effects on binding affinity between Pex5p and other oligomeric proteins should be considered. Our study provides direct thermodynamic data revealing that peptide binding to Pex5p-C binding is favored by lysine in the (-4) position and leucine in the (-5) position. Our results suggest that peptides or proteins with optimized residues in the (-4) and/or (-5) positions can bind to Pex5p with affinities that are at least two orders of magnitude greater than that of YQSKL, and that this stabilization can compensates for otherwise weakly binding PTS1s.
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PMID:Pex5p binding affinities for canonical and noncanonical PTS1 peptides. 1514 84

The response of the antioxidant defense system of an intertidal macroalgae Corallina officinalis L. to different dosages of UV-B irradiation was investigated. Results showed that superoxide dimutase (SOD) and peroxidase (POX) increased and then maintained at a relatively stable level when subjected to UV-B irradiation. Catalase (CAT) activity under medium dosage of UV-B irradiation (Muv) and high dosage of UV-B irradiation (Huv) treatments were significantly decreased. Ascorbate peroxidase (APX) activity first remained unaltered and then increased in Huv treatment. In addition, the assay on isozymes was carried out using non-denaturing polyacrylamide gel electrophoresis (PAGE). The activities of some SOD isoforms were altered by UV-B. Two new bands (POX V and POX VII) appeared upon exposure to all three UV-B dosages. CAT III activity was increased by low dosage of UV-B irradiation (Luv), whereas CAT III and CAT IV disappeared when the alga was exposed to Muv and Huv. Two bands of APX (APX VI and APX VII) were increased and a new band (APX X) was observed under Huv exposure. H2O2 and thiobarbituric acid reacting substance (TBARS) increased under Muv and Huv treatments. Overall, UV-B protection mechanisms are partly inducible and to a certain extent sufficient to prevent the accumulation of damage in C. officinalis.
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PMID:Ultraviolet irradiation induced oxidative stress and response of antioxidant system in an intertidal macroalgae Corallina officinalis L. 2060 8