Larson, T. R. | bioRxiv Science

bioRxiv2021

A functionally conserved STORR gene fusion in Papaver species that diverged 16.8 million years ago

The STORR gene fusion event is considered a key step in the evolution of benzylisoquinoline alkaloid (BIA) metabolism in opium poppy as the resulting bi-modular protein performs the isomerization of (S)- to (R)-reticuline which is required for morphinan biosynthesis. Our previous analysis of the opium poppy genome suggested the STORR gene fusion event occurred before a whole genome duplication event 7.2 million years ago. Here we use a combination of phylogenetic, transcriptomic, metabolomic, biochemical and genomic analysis to investigate the origin of the STORR gene fusion across the Papaveraceae family. The pro-morphinan/morphinan subclass of BIAs was present in a subset of 10 Papaver species including P. somniferum (opium poppy) and this correlated with the presence of the STORR gene fusion with one important exception. P. californicum does not produce morphinans but it does contain a STORR gene fusion that epimerizes (S)- to (R)-reticuline when heterologously expressed in yeast. The high similarity of the amino acid sequence linking the two modules of STORR along with phylogenetic gene tree analysis strongly suggests the gene fusion occurred only once and between 17-25 million years ago before the separation of P. californicum from the other Papaver species. We discovered that the most abundant BIA in P. californicum is (R)-glaucine, a member of the aporphine subclass of BIAs. Only the (S) isomer of this compound has previously been reported from nature. These results lead us to conclude that the function of the STORR gene fusion is not exclusive to morphinan production in the Papaveraceae.

plant biology↗

bioRxiv2020

Membrane linkage of a Streptococcus pneumoniae Wzy capsular polysaccharide occurs through an acylglycerol

Capsular polysaccharides (capsules) protect bacteria from environmental insults and can contribute to virulence in pathogenic bacteria. Their appropriate display on the bacterial surface is critical to their functions. In Gram-positive bacteria, most capsules are synthesized by the Wzy polymerase-dependent pathway, which is also utilized in the synthesis of many capsules and O-antigens of Gram-negative bacteria. Synthesis of capsule repeat units initiates on undecaprenyl-phosphate on the inner face of the cytoplasmic membrane, with polymerization occurring on the outer face of the membrane. In Gram-positive bacteria, the capsule can be transferred to peptidoglycan, as in Streptococcus pneumoniae where a direct glycosidic bond to the peptidoglycan N-acetylglucosamine occurs. In S. pneumoniae, capsule can also be detected on the membrane, and this has generally been assumed to reflect polysaccharide that is linked to undecaprenyl-phosphate and in the process of synthesis. We provide evidence here, however, that final membrane linkage occurs through an acylglycerol, and essentially all of the polysaccharide is transferred from the initial undecaprenyl-phosphate acceptor to an alternate acceptor. This step allows for recycling of undecaprenyl-phosphate and represents an additional terminal step in capsule synthesis. In this regard, capsule synthesis resembles that of the wall- and lipoteichoic acids of S. pneumoniae, wherein a common repeat unit and polymer structure are synthesized by the Wzy pathway with divergence at the terminal step that results in linkages to peptidoglycan and a membrane acylglycerol anchor. IMPORTANCELinkage of capsular polysaccharides to the bacterial cell surface is a critical step in assuring the ability of these polymers to fulfill their functions, such as the resistance to complement-mediated phagocytosis that can be essential for pathogenic organisms to survive in host environments. Knowledge of the mechanisms by which these linkages occur is incomplete. In this study, we provide evidence for linkage of an S. pneumoniae Wzy capsule to an acylglycerol, the most abundant class of lipids in the membrane. This linkage provides a terminal acceptor for capsule that occurs in addition to that of peptidoglycan. Transfer to these terminal receptors is an essential step in CPS synthesis, as failure to do so can be lethal for the cell.

microbiology↗