Vellozone,a tetracyclic triterpene from Vellozia stipitata

The isolation of (20R)-20-hydroxy-24-methylenedammar-3-one from Vellozia stipitata is described.     

PARP1 ADP-ribosylates lysine residues of the core histone tails

The chromatin-associated enzyme PARP1 has previously been suggested to ADP-ribosylate histones, but the specific ADP-ribose acceptor sites have remained enigmatic. Here, we show that PARP1 covalently ADP-ribosylates the amino-terminal histone tails of all core histones. Using biochemical tools and novel electron transfer dissociation mass spectrometric protocols, we identify for the first time K13 of H2A, K30 of H2B, K27 and K37 of H3, as well as K16 of H4 as ADP-ribose acceptor sites. Multiple explicit water molecular dynamics simulations of the H4 tail peptide into the catalytic cleft of PARP1 indicate that two stable intermolecular salt bridges hold the peptide in an orientation that allows K16 ADP-ribosylation. Consistent with a functional cross-talk between ADP-ribosylation and other histone tail modifications, acetylation of H4K16 inhibits ADP-ribosylation by PARP1. Taken together, our computational and experimental results provide strong evidence that PARP1 modifies important regulatory lysines of the core histone tails.     

Identification of an ATP-binding cassette transport system required for translocation of lipopolysaccharide O-antigen side-chains across the cytoplasmic membrane of Klebsiella pneumoniae serotype O1

The rfb_kpO1 gene cluster of Klebsiella pneumoniae O1 directs synthesis of the D-galactan I component of the lipopolysaccharide O-antigen. The first two genes in the rfb_kpO1cluster encode Rrfb_kpO1and RfbB_KpO1, with predicted sizes of 29.5 or 30.0 kDa and 27.4 kDa, respectively. RfbB_KpO1 contains a consensus ATP-binding domain and shares homology with several proteins which function as ATP-binding components of cell surface polysaccharide transporters. RfbA_KpO1 is predicted to be an integral membrane protein with five putative membrane-spanning domains and its transmembrane topology was confirmed by TnphoA mutagenesis. The hydropathy plot of RfbA_KpO1 resembles KpsM, the transcytoplasmic membrane component of the capsular polysaccharide transporter from Escherichia coli K-1 and K-5. These relationships suggest that RfbA_KpO1 and RfbB_KpO1 belong to a family of two-component ABC (ATP-binding cassette) transporters. E. coli K-12 containing a plasmid carrying an rfb_KpO1 gene cluster deleted in rfbA_KpO1 and rfbB_KpO1 expresses rough lipopolysaccharide molecules on its surface and accumulates cytoplasmic O-antigen. When RfbA_KpO1 and RfbB_KpO1 are supplied in trans by a compatible plasmid, O-polysaccharide transport is restored and smooth D-galactan l-substituted lipopolysaccharide is produced. RfbA_KpO1 and RfbB_KpO1 are, therefore, proposed to constitute a system required for transport of D-galactan I across the cytoplasmic membrane, where RfbA_KpO1 represents the membrane-spanning translocator and RfbB_KpO1 couples the energy of ATP hydrolysis to the transport process.