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    Inhibition of Rumen Methanogens by a Novel Archaeal Lytic Enzyme Displayed on Tailored Bionanoparticles.
    (Frontiers Media S.A., 2018-10-09) Altermann E; Schofield LR; Ronimus RS; Beattie AK; Reilly K; Neubauer P
    Methane is a potent greenhouse gas, 25 times more efficient at trapping heat than carbon dioxide. Ruminant methane emissions contribute almost 30% to anthropogenic sources of global atmospheric methane levels and a reduction in methane emissions would significantly contribute to slowing global temperature rises. Here we demonstrate the use of a lytic enyzme, PeiR, from a methanogen virus that infects Methanobrevibacter ruminantium M1 as an effective agent inhibiting a range of rumen methanogen strains in pure culture. We determined the substrate specificity of soluble PeiR and demonstrated that the enzyme is capable of hydrolysing the pseudomurein cell walls of methanogens. Subsequently, peiR was fused to the polyhydroxyalkanoate (PHA) synthase gene phaC and displayed on the surface of PHA bionanoparticles (BNPs) expressed in Eschericia coli via one-step biosynthesis. These tailored BNPs were capable of lysing not only the original methanogen host strain, but a wide range of other rumen methanogen strains in vitro. Methane production was reduced by up to 97% for 5 days post-inoculation in the in vitro assay. We propose that tailored BNPs carrying anti-methanogen enzymes represent a new class of methane inhibitors. Tailored BNPs can be rapidly developed and may be able to modulate the methanogen community in vivo with the aim to lower ruminant methane emissions without impacting animal productivity.
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    Structural characterization of a PCP-R didomain from an archaeal nonribosomal peptide synthetase reveals novel interdomain interactions
    (Elsevier Inc on behalf of American Society for Biochemistry and Molecular Biology, 2021-02-17) Deshpande S; Altermann E; Sarojini V; Lott JS; Lee TV; Jez J
    Nonribosomal peptide synthetases (NRPSs) are multimodular enzymes that produce a wide range of bioactive peptides, such as siderophores, toxins, and antibacterial and insecticidal agents. NRPSs are dynamic proteins characterized by extensive interdomain communications as a consequence of their assembly-line mode of synthesis. Hence, crystal structures of multidomain fragments of NRPSs have aided in elucidating crucial interdomain interactions that occur during different steps of the NRPS catalytic cycle. One crucial yet unexplored interaction is that between the reductase (R) domain and the peptide carrier protein (PCP) domain. R domains are members of the short-chain dehydrogenase/reductase family and function as termination domains that catalyze the reductive release of the final peptide product from the terminal PCP domain of the NRPS. Here, we report the crystal structure of an archaeal NRPS PCP-R didomain construct. This is the first NRPS R domain structure to be determined together with the upstream PCP domain and is also the first structure of an archaeal NRPS to be reported. The structure reveals that a novel helix-turn-helix motif, found in NRPS R domains but not in other short-chain dehydrogenase/reductase family members, plays a major role in the interface between the PCP and R domains. The information derived from the described PCP-R interface will aid in gaining further mechanistic insights into the peptide termination reaction catalyzed by the R domain and may have implications in engineering NRPSs to synthesize novel peptide products.