Biology subjects

Saalbach, G.

Publications and source records attributed to Saalbach, G..

2 recordsLinked to original sources

bioRxiv2018

Uncoupled activation and cyclisation in catmint reductive terpenoid biosynthesis

Terpene synthases typically form complex molecular scaffolds by concerted activation and cyclization of linear starting materials in a single enzyme active site. Here we show that iridoid synthase, an atypical reductive terpene synthase, catalyses the activation of its substrate 8-oxogeranial into a reactive enol intermediate but does not catalyse the subsequent cyclisation into nepetalactol. This discovery led us to identify a class of nepetalactol-related short-chain dehydrogenase enzymes (NEPS) from catmint (Nepeta mussinii) which catalyse the stereoselective cyclisation of the enol intermediate into nepetalactol isomers. Subsequent oxidation of nepetalactols by NEPS1 provides nepetalactones, metabolites that are well known for both insect-repellent activity and euphoric effect in cats. Structural characterisation of the NEPS3 cyclase reveals it binds to NAD+ yet does not utilise it chemically for a non-oxidoreductive formal [4+2] cyclisation. These discoveries will complement metabolic reconstructions of iridoid and monoterpene indole alkaloid biosynthesis.

biochemistry↗

bioRxiv2016

Ubiquitylation activates a peptidase that promotes cleavage and destabilization of its activating E3 ligases and diverse growth regulatory proteins to limit cell proliferation in Arabidopsis

The characteristic shapes and sizes of organs are established by cell proliferation patterns and final cell sizes, but the underlying molecular mechanisms coordinating these are poorly understood. Here we characterize a ubiquitin-activated peptidase called DA1 that limits the duration of cell proliferation during organ growth in Arabidopsis thaliana. The peptidase is activated by two RING E3 ligases, BB and DA2, which are subsequently cleaved by the activated peptidase and destabilized. In the case of BB, cleavage leads to destabilization by the RING E3 ligase PRT1 of the N-end rule pathway. DA1 peptidase activity also cleaves the de-ubiquitylase UBP15, which promotes cell proliferation, and the transcription factors TCP15 and TCP22, which promote cell proliferation proliferation and repress endoreduplication. We propose that DA1 peptidase activity regulates the duration of cell proliferation and the transition to endoreduplication and differentiation during organ formation in plants by coordinating the destabilization of regulatory proteins.

plant biology↗