Evidence for a cytochrome bcc–aa 3 interaction in the respiratory chain of Mycobacterium smegmatis

Abstract

Spectroscopic analysis of membranes isolated from Mycobacterium smegmatis, along with analysis of its genome, indicates that the cytochrome c branch of its respiratory pathway consists of a modified bc 1 complex that contains two cytochromes c in its c 1 subunit, similar to other acid-fast bacteria, and an aa 3-type cytochrome c oxidase. A functional association of the cytochrome bcc and aa 3 complexes was indicated by the findings that levels of detergent sufficient to completely disrupt isolated membranes failed to inhibit quinol-driven O2 reduction, but known inhibitors of the bc 1 complex did inhibit quinol-driven O2 reduction. The gene for subunit II of the aa 3-type oxidase indicates the presence of additional charged residues in a predicted extramembrane domain, which could mediate an intercomplex association. However, high concentrations of monovalent salts had no effect on O2 reduction, suggesting that ionic interactions between extramembrane domains do not play the major role in stabilizing the bcc–aa 3 interaction. Divalent cations did inhibit electron transfer, likely by distorting the electron-transfer interface between cytochrome c 1 and subunit II. Soluble cytochrome c cannot donate electrons to the aa 3-type oxidase, even though key cytochrome c-binding residues are conserved, probably because the additional residues of subunit II prevent the binding of soluble cytochrome c. The results indicate that hydrophobic interactions are the primary forces maintaining the bcc–aa 3 interaction, but ionic interactions may assist in aligning the two complexes for efficient electron transfer.

Cytochrome <b><i>bcc-aa3</i></b> Oxidase Supercomplexes in the Aerobic Respiratory Chain of <b><i>Streptomyces coelicolor</i></b> A3(2)

“…[Matsoso et al, 2005;Megehee et al, 2006;Kim et al, 2015]. To provide further evidence in support of this suggestion, we separated protein complexes in solubilized membrane fractions derived from spores (Fig.…”

“…1). Early studies performed with C. glutamicum, and more recently with M. tuberculosis and M. smegmatis, have revealed that these two large enzyme complexes form a bcc-aa 3 supercomplex Megehee et al, 2006;Kim et al, 2015;Kao et al, 2016], which is necessary if a soluble c-type cytochrome component is lacking [Niebisch and Bott, 2001;Sakamoto et al, 2001;Sone et al, 2001].…”

Regulation of the ald Gene Encoding Alanine Dehydrogenase by AldR in Mycobacterium smegmatis

“…We also observed that expression of ald was increased by 27% relative to that of the control when M. smegmatis cells were treated with 500 M CN Ϫ (data not shown). There are two functional terminal oxidases in the ETC of M. smegmatis, aa 3 cytochrome c oxidase and bd quinol oxidase (46,47). The activity of aa 3 cytochrome c oxidase is inhibited by NO and CN Ϫ , while bd-type quinol oxidase is insensitive to CN Ϫ (46).…”

Interaction between Cytochrome caa3 and F1F0-ATP Synthase of Alkaliphilic Bacillus pseudofirmus OF4 Is Demonstrated by Saturation Transfer Electron Paramagnetic Resonance and Differential Scanning Calorimetry Assays

“…A candidate of interest in the cytochrome caa 3 is the unusually acidic patch that was noted when the operon encoding the complex was first cloned and sequenced (17). This acidic domain is predicted to be near the region of subunit II just above where the pumped protons are modeled to emerge (50,51). Also of interest will be the roles of specific membrane lipids, especially cardiolipin (8), and additional respiratory chain components in supercomplex formation or proton transfer.…”