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B21-High Throughput SAXS	Structure and mechanism of a phage-encoded SAM lyase revises catalytic function of enzyme family Xiaohu Guo , Annika Soderholm , Sandesh Kanchugal Puttaswamy , Geir V Isaksen , Omar Warsi , Ulrich Eckhard , Silvia Triguis , Adolf Gogoll , Jon Jerlström-Hultqvist , Johan Åqvist , Dan I. Andersson , Maria Selmer Elife 10 DOI: 10.7554/eLife.61818 Diamond Proposal Number(s): [11171] Open Access Show Abstract ▼ Abstract: The first S-adenosyl methionine (SAM) degrading enzyme (SAMase) was discovered in bacteriophage T3, as a counter-defense against the bacterial restriction-modification system, and annotated as a SAM hydrolase forming 5’-methyl-thioadenosine (MTA) and L-homoserine. From environmental phages, we recently discovered three SAMases with barely detectable sequence similarity to T3 SAMase and without homology to proteins of known structure. Here, we present the very first phage SAMase structures, in complex with a substrate analogue and the product MTA. The structure shows a trimer of alpha–beta sandwiches similar to the GlnB-like superfamily, with active sites formed at the trimer interfaces. Quantum-mechanical calculations, thin-layer chromatography, and nuclear magnetic resonance spectroscopy demonstrate that this family of enzymes are not hydrolases but lyases forming MTA and L-homoserine lactone in a unimolecular reaction mechanism. Sequence analysis and in vitro and in vivo mutagenesis support that T3 SAMase belongs to the same structural family and utilizes the same reaction mechanism.	Feb 2021

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B21-High Throughput SAXS

Structure and mechanism of a phage-encoded SAM lyase revises catalytic function of enzyme family