Accumulation of pre-apocytochrome f in a Synechocystis sp. PCC 6803 mutant impaired in cytochrome c maturation

Martin Tichy, Willem Vermaas

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Cytochrome c maturation involves heme transport and covalent attachment of heme to the apoprotein. The 5' end of the ccsB gene, which is involved in the maturation process and resembles the ccs1 gene from Chlamydomonas reinhardtii, was replaced by a chloramphenicol resistance cartridge in the cyanobacterium Synechocystis sp. PCC 6803. The resulting Δ(M1-A24) mutant lacking the first 24 ccsB codons grew only under anaerobic conditions. The mutant retained about 20% of the wild-type amount of processed cytochrome f with heine attached, apparently assembled in a functional cytochrome b6f complex. Moreover, the mutant accumulated unprocessed apocytochrome f in its membrane fraction. A pseudorevertant was isolated that regained the ability to grow under aerobic conditions. The locus of the second-site mutation was mapped to ccsB, and the mutation resulted in the formation of a new potential start codon in the intergenic region, between the chloramphenicol resistance marker and ccsB, in frame with the remaining part of ccsB. In this pseudorevertant the amount of holocyt f increased, whereas that of unprocessed apocytochrome f decreased. We suggest that the original deletion mutant Δ(M1-A24) expresses an N-terminally truncated version of the protein. The stable accumulation of unprocessed apocytochrome f in membranes of the Δ(M1-A24) mutant may be explained by its association with truncated and only partially functional CcsB protein resulting in protection from degradation. Our attempt to delete the first 244 codons of ccsB in Synechocystis sp. PCC 6803 was not successful, suggesting that this would lead to a lack of functional cytochrome b6f complex. The results suggest that the CcsB protein is an apocytochrome chaperone, which together with CcsA may constitute part of cytochrome c lyase.

Original languageEnglish (US)
Pages (from-to)32396-32401
Number of pages6
JournalJournal of Biological Chemistry
Volume274
Issue number45
DOIs
StatePublished - Nov 5 1999

Fingerprint

Cytochromes f
Synechocystis
Cytochromes c
Cytochrome b6f Complex
Chloramphenicol Resistance
Chloramphenicol
Heme
Codon
Genes
Membranes
Chlamydomonas reinhardtii
Mutation
Proteins
Intergenic DNA
Apoproteins
Lyases
Initiator Codon
Cyanobacteria
Association reactions
Degradation

ASJC Scopus subject areas

  • Biochemistry

Cite this

Accumulation of pre-apocytochrome f in a Synechocystis sp. PCC 6803 mutant impaired in cytochrome c maturation. / Tichy, Martin; Vermaas, Willem.

In: Journal of Biological Chemistry, Vol. 274, No. 45, 05.11.1999, p. 32396-32401.

Research output: Contribution to journalArticle

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abstract = "Cytochrome c maturation involves heme transport and covalent attachment of heme to the apoprotein. The 5' end of the ccsB gene, which is involved in the maturation process and resembles the ccs1 gene from Chlamydomonas reinhardtii, was replaced by a chloramphenicol resistance cartridge in the cyanobacterium Synechocystis sp. PCC 6803. The resulting Δ(M1-A24) mutant lacking the first 24 ccsB codons grew only under anaerobic conditions. The mutant retained about 20{\%} of the wild-type amount of processed cytochrome f with heine attached, apparently assembled in a functional cytochrome b6f complex. Moreover, the mutant accumulated unprocessed apocytochrome f in its membrane fraction. A pseudorevertant was isolated that regained the ability to grow under aerobic conditions. The locus of the second-site mutation was mapped to ccsB, and the mutation resulted in the formation of a new potential start codon in the intergenic region, between the chloramphenicol resistance marker and ccsB, in frame with the remaining part of ccsB. In this pseudorevertant the amount of holocyt f increased, whereas that of unprocessed apocytochrome f decreased. We suggest that the original deletion mutant Δ(M1-A24) expresses an N-terminally truncated version of the protein. The stable accumulation of unprocessed apocytochrome f in membranes of the Δ(M1-A24) mutant may be explained by its association with truncated and only partially functional CcsB protein resulting in protection from degradation. Our attempt to delete the first 244 codons of ccsB in Synechocystis sp. PCC 6803 was not successful, suggesting that this would lead to a lack of functional cytochrome b6f complex. The results suggest that the CcsB protein is an apocytochrome chaperone, which together with CcsA may constitute part of cytochrome c lyase.",
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