Characterization of the cytochrome bc1 complex pet genes from chromatium vinosum

This research is focused on three different regions of the genome of the purple sulfur bacterium Chromatium vinosun: (1) Characterization of the pet operon, coding for the three subunits of the cytochrome bc1 complex of C vinosum, (2) Characterization of the ccll and helX genes encoding cytochrome c heme lyase and a thioredoxin-like protein of C. vinosum, respectively. These two gene products are essential for cytochrome e biogenesis. (3) Characterization of C vinosumpurH, IpxA, and purD genes encoding the bifunctional enzyme 5'-phosphoribosyl 5-aminoimidazole-4-carboxamide (AICAR) formyltransferase/GMP cyclohydrolase, the UDP-iV-acetylglucosamine O-acyltransferase, and the 5’-phosphoribosyl-glycinamide (GAR) synthetase, respectively. Both the purH and purD gene products are essential for purine biosynthesis. The IpxA gene product is essential for lipid A biosynthesis.

Ubiquinol: cytochrome elc2 oxidoreductase, also known as the cytochrome bcj complex, is a membrane-bound protein with multiple subunits that is widely distributed among diverse families of organisms. It is present in eukaryotic mitochondria for respiratory electron transport, and in photosynthetic bacteria and aerobic bacteria for photosynthetic electron transport or respiratory electron transport. This enzyme catalyzes electron flow from ubiquinol to cytochrome c (ci) generating a proton gradient which is coupled to ATP production and other processes involved in energy utilization. In this work, portions of the structural genes for the Rieske iron-sulfur protein and cytochrome b subunits of the cytochrome bci complex of C. vinosum have been cloned and both strands sequenced. The organization of the genes coding for the prosthetic group-containing subunits of the C. vinosum cytochrome bci complex is similar to that reported previously for the pet operon of photosynthetic purple non-sulfur bacteria. The amino acid sequence deduced from partial sequences of the petAB genes show homology to the Rieske iron sulfur proteins and cytochrome b subunits of photosynthetic purple non-sulfur bacteria.

Cytochrome c heme lyase catalyzes the ligation of heme to apocytochrome c during cytochrome c biogenesis. The thioredoxin-like protein maintains the cysteine residues of apocytochrome c in their reduced state for heme ligation. Portions of the sturctural gene for the cytochrome c heme lyase and the full-length gene for the thioredoxin-like protein of C. vinosum have been cloned and both strands sequenced. The deduced amino acid sequence of the C vinosum cell gene shows homology to the corresponding protein encoded by Rb. capsulatus ceil gene, the protein encoded by E. coli cemF (yejR) gene, the protein encoded by the H influenzae cemF gene, the cycK gene product ofB. japonicum, R. meliloti, and R. leguminosarum, and the cyt4 gene product of Pseudomonas fluorescens. The deduced amino acid sequence of the helX gene of C vinosum shows homology to the corresponding thioredoxin-like proteins encoded by the Rb. capulatus helX gene, the B. japonicum tlpB gene, the E. coli cemG iyejQ) gene, the P. fluorescens cyt5 gene, the H. influenzae dsel and dse2 genes, and the K leguminosarum cycY gene

The purH gene product catalyzes both step 9 and step 10 of the purine nucleotide biosynthesis. The IpxA gene product catalyzes the first step of lipidA biosynthesis. The purD gene product catalyzes the second step of the purine nucleotide biosynthesis. Portions of the C vinosum purH gene, the full-length IpxA gene, and portions of the purD gene have been cloned and both strands sequenced. The C. vinosum purH gene shows homology to the purH gene of £•. coli and Salmonella typhimurium at both the nucleotide and deduced amino acid levels. The IpxA gene of C vinosum shows homology to the IpxA gene of 5. typhimurium, E. coli. Yersinia enterocoeitica, and Rickettisia rickettsii at both the nucleotide and deduced amino acid levels. The purD gene of C vinosum shows homology to the purD gene ofE. coli and S. typhimurium at both the nucleotide and deduced amino acid levels.