دانلود رایگان مقاله مجموعه بزرگ تنفسی اجباری از اکتینوباکتریا

ABSTRACT

Actinobacteria are closely linked to human life as industrial producers of bioactive molecules and as human pathogens. Respiratory cytochrome bcc complex and cytochrome aa3 oxidase are key components of their aerobic energy metabolism. They form a supercomplex in the actinobacterial species Corynebacterium glutamicum. With comprehensive bioinformatics and phylogenetic analysis we show that genes for cyt bcc-aa3 supercomplex are characteristic for Actinobacteria (Actinobacteria and Acidimicrobiia, except the anaerobic orders Actinomycetales and Bifidobacteriales). An obligatory supercomplex is likely, due to the lack of genes encoding alternative electron transfer partners such as mono-heme cyt c. Instead, subunit QcrC of bcc complex, here classified as short di-heme cyt c, will provide the exclusive electron transfer link between the complexes as in C. glutamicum. Purified to high homogeneity, the C. glutamicum bcc-aa3 supercomplex contained all subunits and cofactors as analyzed by SDSPAGE, BN-PAGE, absorption and EPR spectroscopy. Highly uniform supercomplex particles in electron microscopy analysis support a distinct structural composition. The supercomplex possesses a dimeric stoichiometry with a ratio of a-type, b-type and c-type hemes close to 1:1:1. Redox titrations revealed a low potential bcc complex (EmISP = +160 mV, EmbL = −291 mV, EmbH = −163 mV, Em cc = +100 mV) fined-tuned for oxidation of menaquinol and a mixed potential aa3 oxidase (Em CuA = +150 mV, Em a/a3 = +143/+317 mV) mediating between low and high redox potential to accomplish dioxygen reduction. The generated molecular model supports a stable assembled supercomplex with defined architecture which permits energetically efficient coupling of menaquinol oxidation and dioxygen reduction in one supramolecular entity.

4. Conclusion

We show that characteristic for Actinobacteria is the genetic composition for a respiratory supercomplex that is comprised of cyt bcc complex and cyt aa3 oxidase. It is likely to be an obligatory supercomplex due to the lack of genes encoding alternative electron transfer partners. This bcc-aa3 supercomplex is present in almost all actinobacterial species that are capable of aerobic metabolism. Based on characterization of the supercomplex from C. glutamicum, it combines a low potential bcc complex and a mixed potential aa3 oxidase in defined spatial arrangement constrained by an indispensable short di-heme QcrC, thus facilitating energetically highly efficient coupled menaquinol oxidation and dioxygen reduction. Future studies need to elucidate the structural basis of redox tuning and the structural composition of the supercomplex. The actinobacterial supercomplex is of interest for improving efficiency of industrial production strains or for development of drugs against pathogens.