Cloning and sequencing of the gene encoding the [2Fe-2S] ferredoxin from Clostridium pasteurianum

Heterologous overproduction of 2[4Fe4S]- and [2Fe2S]-type clostridial ferredoxins and [2Fe2S]-type agrobacterial ferredoxin

Ferredoxins are small, acidic proteins containing iron-sulfur clusters that are widespread in living organisms. They play key roles as electron carriers in various metabolic processes, including respiration, photosynthesis, fermentation, nitrogen fixation, carbon dioxide fixation, and hydrogen production. However, only several kinds of ferredoxins are commercially available now, greatly limiting the investigation of ferredoxin-related enzymes and metabolic processes. Here we describe the heterologous overproduction of 2[4Fe4S]- and [2Fe2S]-type clostridial ferredoxins and [2Fe2S]-type agrobacterial ferredoxin. Adding extra iron and sulfur sources to the medium in combination with using Escherichia coli C41(DE3) harboring pCodonplus and pRKISC plasmids as host greatly enhanced iron-sulfur cluster synthesis in the three ferredoxins. After induction for 12 h in terrific broth and purification by affinity chromatography and anion exchange chromatography, approximately 3.4 mg of streptavidin (Strep)-tagged and 3.7 mg of polyhistidine (His)-tagged clostridial 2[4Fe4S] ferredoxins were obtained from 1 l of culture. Excitingly, after induction for 24 h in terrific broth, around 40 mg of His-tagged clostridial [2Fe2S] and 23 mg of His-tagged agrobacterial [2Fe2S] ferredoxins were purified from 1 l of culture. The recombinant ferredoxins apparently exhibited identical properties and physiological function to native ferredoxins. No negative impact of two different affinity tags on ferredoxin activity was found. In conclusion, we successfully developed a convenient method for heterologous overproduction of the three kinds of ferredoxins with satisfactory yields and activities, which would be very helpful for the ferredoxin-related researches.

Ferredoxins of the third kind

Most low-potential ferredoxins (Fds) are of the well-known [2Fe-2S] plant or [4Fe-4S] bacterial type. Yet, an additional class of [2Fe-2S] Fds has been recognized on the basis of sequence and spectroscopic idiosyncrasies. A recent crystal structure has confirmed the uniqueness of this third kind of Fd, and shown that these proteins display an unexpected structural similarity to thioredoxin. The properties of these thioredoxin-like [2Fe-2S] Fds are summarized, and hypotheses concerning their function are discussed.

The structure of iron-sulfur proteins

Ferredoxins are a group of iron-sulfur proteins for which a wealth of structural and mutational data have recently become available. Previously unknown structures of ferredoxins which are adapted to halophilic, acidophilic or hyperthermophilic environments and new cysteine patterns for cluster ligation and non-cysteine cluster ligation have been described. Site-directed mutagenesis experiments have given insight into factors that influence the geometry, stability, redox potential, electronic properties and electron-transfer reactivity of iron-sulfur clusters.

Cobalamin (vitamin B12) biosynthesis: identification and characterization of a Bacillus megaterium cobI operon

A 16 kb DNA fragment has been isolated from a Bacillus megaterium genomic library and fully sequenced. The fragment contains 15 open reading frames, 14 of which are thought to constitute a B. megaterium cobalamin biosynthetic (cob) operon. Within the operon, 11 genes display similarity to previously identified Salmonella typhimurium cobalamin biosynthetic genes (cbiH60, -J, -C, -D, -ET, -L, -F, -G, -A, cysGA and btuR), whereas three do not (cbiW, -X and -Y). The genes of the B. megaterium cob operon were compared with the cobalamin biosynthetic genes of Pseudomonas denitrificans, Methanococcus jannaschii and Synechocystis sp. Taking into account the presence of cbiD and cbiG, the absence of a cobF, cobG and cobN, -S and -T, it was concluded that B. megaterium, M. jannaschii and Synechocystis sp., like S. typhimurium, synthesize cobalamin by an anaerobic pathway, in which cobalt is added at an early stage and molecular oxygen is not required.

Physical and genetic map of the Clostridium acetobutylicum ATCC 824 chromosome

A physical and genetic map of the Clostridium acetobutylicum ATCC 824 chromosome was constructed. The macrorestriction map for CeuI, EagI, and SstII was created by ordering the 38 restriction sites by one- and two-dimensional pulsed-field gel electrophoresis (PFGE) and by using an original strategy based on the CeuI enzyme and indirect end labelling by hybridization on both sides of the CeuI sites with rrs (16S RNA) and 3' rrl (23S RNA) probes. The circular chromosome was estimated to be 4.15 Mb in size, and the average resolution of the physical map is 110 kb. The chromosome contains 11 rrn loci, which are localized on 44% of the chromosome in a divergent transcriptional orientation regarding the presumed location of the replication origin. In addition to these 11 rrn operons, a total of 40 identified genes were mapped by hybridization experiments with genes from C. acetobutylicum and from various other clostridia as probes. The genetic map of C. acetobutylicum was compared to that of the three other endospore-forming bacteria characterized so far: Bacillus subtilis, Clostridium beijerinckii, and Clostridium perfringens. Parodoxically, the chromosomal backbone of C. acetobutylicum showed more similarity to that of B. subtilis than to those of the clostridia.

Physical map of the Clostridium beijerinckii (formerly Clostridium acetobutylicum) NCIMB 8052 chromosome

A combined physical and genetic map of the single, circular, 6.7-Mbp chromosome of the NCIMB 8052 strain of Clostridium beijerinckii (formerly Clostridium acetobutylicum) has been constructed by using a combination of cloned DNA fragments as hybridization probes and a bank of strains harboring insertions of the conjugative transposon Tn1545. The positions of 81 restriction endonuclease cleavage sites and 32 genes have been determined. Eight genes concerned with solventogenic fermentation are found at three different locations. The chromosome contains at least 13 rrn operons, 11 of which have been located on the map. Their transcriptional orientation diverges from the presumed location of the replication origin.

Characterisation of a complementary DNA encoding a novel plant enzyme with sucrolytic activity

The cloning of a 1332 bp cDNA from a potato (Solanum tuberosum L.) cv. Cara leaf cDNA expression library, using an antibody raised against a purified tuber protein preparation with sucrolytic activity, is described. The corresponding gene in potato is of low copy number, is expressed in a variety of tissues, and encodes a protein which includes several domains with similarity to database sequences, including ferredoxin from Clostridium pasteurianum. Expression of the cDNA in E. coli yields a fusion protein with sucrolytic activity.