6qmm

Publication Abstract from PubMed

Spermidine is a ubiquitious polyamine synthesised by spermidine synthase (SPDS) from the substrates putrescine and decarboxylated S-adenosylmethionine (dcAdoMet). SPDS generally is active as homodimer but higher oligomerization states have been reported in SPDS from thermophiles, which are less specific to putrescine as the amino acceptor substrate. Several crystal structures of SPDS have been solved with and without bound substrates and/or products, as well as inhibitors. Here, we determined the crystal structure of SPDS from the cyanobacterium Synechococcus ( Sy SPDS) that is a homodimer, which we also observed in solution. Unlike crystal structures reported for bacterial and eukaryotic SPDS with bound ligands, Sy SPDS structure not only has bound putrescine substrate taken from the expression host, but also spermidine product most likely as a result of an enzymatic reaction. Hence, to our knowledge, this is the first structure reported with both amino ligands in the same structure. Interestingly, the gate-keeping loop is disordered in the putrescine-bound monomer while it is stabilised in the spermidine-bound monomer of the Sy SPDS dimer. This confirms the gate-keeping loop as the key structural element that prepares the active site upon binding of dcAdoMet for the catalytic reaction of the amine donor and putrescine.

Crystal structure of dimeric Synechococcus Spermidine Synthase with bound polyamine substrate and product.,Guedez G, Pothipongsa A, Siren S, Liljeblad A, Jantaro S, Incharoensakdi A, Salminen TA Biochem J. 2019 Mar 15. pii: BCJ20180811. doi: 10.1042/BCJ20180811. PMID:30877192^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.