Chemistry seminar-Biosynthesis of copper-binding natural products by multi-iron enzymes

Thursday, October 24th @ 3:30 pm in ESSC 255

Methanobactins (Mbns) are ribosomally synthesized, post-translationally modified peptide (RiPP) natural products produced by methane-oxidizing bacteria to acquire copper from the environment. Due to their high affinity for Cu(I), Mbns are currently under investigation as therapeutics for Wilson disease, a genetic disorder of copper metabolism. In Mbn biosynthesis, two cysteine residues in the precursor peptide, MbnA, are modified to paired oxazolone/thioamide groups by an iron-containing heterodimer of the MbnB and MbnC proteins (MbnBC). MbnB is the founding member of the multinuclear nonheme iron-dependent oxidase (MNIO) family, now implicated in the biosynthesis of multiple RiPPs, and MbnC includes a RiPP recognition element. Site-directed mutagenesis and multiple crystal structures identify the locations of three Fe binding sites in MbnB and the molecular basis for MbnA recognition by MbnC. Advanced paramagnetic spectroscopic and biochemical studies of MbnBC indicate that the active species is a mixed valent Fe(II)Fe(III) cluster that binds MbnA via its Fe(III) ion. These studies provide a roadmap for characterizing newly discovered MNIOs, including HvfB from nontypeable Haemophilus influenzae, a human pathogen that causes ear and lung infections. HvfB, together with its partner protein HvfC, installs six oxazolone/thioamide groups on HvfA, the precursor peptide to a virulence factor that, like Mbn, binds Cu(I) with high affinity. Understanding the roles of these MNIOs in natural product biosynthesis will provide new avenues for the development of therapeutics.

Biological Sciences seminar - Seeing copper enzymes in their native membrane environment  

Friday, October 25th @ 3 pm in ESSC 255

Aerobic microbial processes are essential sources and sink for greenhouse gases, with methane-oxidizing bacteria (methanotrophs) consuming methane and ammonia-oxidizing bacteria (nitrifiers) releasing nitrous oxide. Methanotrophs and nitrifiers use copper-dependent membrane monooxygenases to carry out the first steps in their metabolisms: the conversions of methane to methanol by particulate methane monooxygenase (pMMO) and ammonia to hydroxylamine by ammonia monooxygenase (AMO). Due to the loss of enzymatic activity upon detergent solubilization from their native intracytoplasmic membranes (ICMs), elucidating the structures and mechanisms of pMMO and AMO has posed significant challenges. Both enzymes have three subunits: PmoB/AmoB, PmoA/AmoA, and PmoC/AmoC. Despite the availability of multiple crystal and cryoelectron microscopy (cryoEM) structures, the location and nature of the pMMO copper active site remain controversial. Attempts to study AMO have not been successful, leaving details of its molecular architecture and copper centers unknown. Using cryoEM single particle analysis, we have visualized both pMMO and AMO directly in their native ICMs at high resolution. These in situ structures reveal the arrangement of enzyme trimers in the membrane, details of the copper centers, bound lipids, and previously unobserved components. The ability to obtain molecular-level insight within the native environment will enable further understanding of these and other environmentally important membrane-bound cuproenzymes.