Evidence for a cytochrome bcc-aa3 interaction in the respiratory chain of Mycobacterium smegmatis

• Published in: Microbiology (Society for General Microbiology) 2006-03, Vol.152 (3), p.823-829
• Main Authors: Megehee, James A, Hosler, Jonathan P, Lundrigan, Michael D
• Format: Article
• Language: English
• Subjects: Bacteriology; Biological and medical sciences; Cell Membrane - enzymology; Electron Transport; Electron Transport Complex III - genetics; Electron Transport Complex III - metabolism; Electron Transport Complex IV - genetics; Electron Transport Complex IV - metabolism; Fundamental and applied biological sciences. Psychology; Hydrophobic and Hydrophilic Interactions; Metabolism. Enzymes; Microbiology; Mycobacterium smegmatis - genetics; Mycobacterium smegmatis - metabolism; Mycobacterium smegmatis - physiology; Oxygen Consumption
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.28723-0

1 Department of Microbiology, The University of Mississippi Medical Center, Jackson, 2500 North State Street, MS 39216-4505, USA 2 Department of Biochemistry, The University of Mississippi Medical Center, Jackson, 2500 North State Street, MS 39216-4505, USA Correspondence Michael D. Lundrigan mlundrigan{at}microbio.umsmed.edu 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 O 2 reduction, but known inhibitors of the bc 1 complex did inhibit quinol-driven O 2 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 O 2 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. Abbreviations: DM, dodecyl - D -maltoside; DMNQ, dimethylnaphthoquinone; DMNQH 2 , dimethylnaphthoquinol; TMPD, N,N,N',N' -tetramethyl- p -phenylenediamine Present address: Center for Infectious Disease and Vaccinology, The Biodesign Institute, Arizona State University, PO Box 875401, Tempe, AZ 85287, USA.