Crystal structure of the C-terminal fragment of NS1 protein from yellow fever virus

Dear Editor,Yellow fever(YF),a mosquito-borne flavivirus disease,is endemic in tropical areas of Africa and Central and South America.YF is transmitted via the bite of infected Aedes aegypti or Haemogogus mosquitoes and mainly affects humans and nonhuman primates.The clinical course of infection in humans shows a wide spectrum of severity including no symptoms,mild illness,and severe disease including

P450-mediated dehydrotyrosine formation during WS9326 biosynthesis proceeds via dehydrogenation of a specific acylated dipeptide substrate

WS9326A is a peptide antibiotic containing a highly unusual N-methyl-E-2-3-dehydrotyrosine(NMet-Dht)residue that is incorporated during peptide assembly on a non-ribosomal peptide synthetase(NRPS).The cytochrome P450 encoded by sas16(P450Sas)has been shown to be essential for the formation of the alkene moiety in NMet-Dht,but the timing and mechanism of the P450Sas-mediatedα,β-dehydrogenation of Dht remained unclear.Here,we show that the substrate of P450Sas is the NRPS-associated peptidyl carrier protein(PCP)-bound dipeptide intermediate(Z)-2-pent-1′-enyl-cinnamoyl-Thr-N-Me-Tyr.We demonstrate that P450Sas-mediated incorporation of the double bond follows N-methylation of the Tyr by the N-methyl transferase domain found within the NRPS,and further that P450Sas appears to be specific for substrates containing the(Z)-2-pent-1’-enyl-cinnamoyl group.A crystal structure of P450Sas reveals differences between P450Sas and other P450s involved in the modification of NRPS-associated substrates,including the substitution of the canonical active site alcohol residue with a phenylalanine(F250),which in turn is critical to P450Sas activity and WS9326A biosynthesis.Together,our results suggest that P450Sas catalyses the direct dehydrogenation of the NRPS-bound dipeptide substrate,thus expanding the repertoire of P450 enzymes that can be used to produce biologically active peptides.