Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hetR gene plays a very important role in cell differentiation of heterocystous cyanobacteria. To understand the mechanism of the hetR gene product in regulation of heterocyst differentiation, the recombinant HetR protein (rHetR) was overproduced in Escherichia coli. Purified rHetR was unstable and degraded easily in solution. Phenylmethanesulfonyl fluoride, a serine-type protease inhibitor, prevented the degradation and was shown to modify covalently rHetR. Dansyl fluoride (DnsF), another serine-type protease inhibitor, also covalently modifies rHetR as shown by electrophoresis and electroblotting of the labeled rHetR and by MS. The labeling of rHetR with phenylmethanesulfonyl fluoride and DnsF was at the same site of rHetR and required Ca2+. S179N-rHetR, a mutant protein from strain 216 of Anabaena PCC 7120, which cannot differentiate heterocysts because of the mutation, was also overproduced and characterized. Although S170N-rHetR still can be labeled with DnsF, no proteolysis was observed, suggesting that Ser179 is involved in proteolytic activity. DnsF-labeled rHetR was digested with trypsin, and the labeled peptide was isolated and sequenced. The labeled peptide matches a sequence from HetR. These results show that HetR is a protease.
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PMID:Evidence that HetR protein is an unusual serine-type protease. 956 Feb 10

HetR is a serine-type protease required for heterocyst differentiation in heterocystous cyanobacteria under conditions of nitrogen deprivation. We have identified the active Ser residue of HetR from Anabaena sp. strain PCC 7120 by site-specific mutagenesis. By changing the S152 residue to an Ala residue, the mutant protein cannot be labeled by Dansyl fluoride, a specific serine-type protein inhibitor. The mutant protein showed no autodegradation in vitro. The mutant hetR gene was introduced into Anabaena strain 884a, a hetR mutant. The resultant strain, Anabaena strain S152A, could not form heterocysts under conditions of nitrogen deprivation even though the up-regulation of the mutant hetR gene was induced upon removal of combined nitrogen. The Anabaena strain 216, which carries a mutant hetR gene encoding S179N HetR and could not form heterocysts, also produced HetR protein upon induction. Sequence comparison shows that Ser152 is conserved in all cyanobacterial HetR. Immunoblotting was used to study HetR induction in both the wild-type and mutant strains. The amount of mutant HetR in strain S152A and in strain 216 increased continuously for 24 h after nitrogen step-down, while the amount of HetR in wild-type cells reached a maximum level within 6 h after nitrogen step-down. Our results show the Ser152 is the active site of HetR. The protease activity is required for heterocyst differentiation and might be needed for repression of HetR overproduction under conditions of nitrogen deprivation.
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PMID:Identification of the active site of HetR protease and its requirement for heterocyst differentiation in the cyanobacterium Anabaena sp. strain PCC 7120. 1069 62