Structural Insights into Thioether Bond Formation in the Biosynthesis of Sactipeptides

Sactipeptides are ribosomally synthesized peptides that contain a characteristic thioether bridge (sactionine bond) that is installed posttranslationally and is absolutely required for their antibiotic activity. Sactipeptide biosynthesis requires a unique family of radical SAM enzymes, which contain multiple [4Fe-4S] clusters, to form the requisite thioether bridge between a cysteine and the α-carbon of an opposing amino acid through radical-based chemistry. Here we present the structure of the sactionine bond-forming enzyme CteB, from Clostridium thermocellum ATCC 27405, with both SAM and an N-terminal fragment of its peptidyl-substrate at 2.04 Å resolution. CteB has the (β/α)6-TIM barrel fold that is characteristic of radical SAM enzymes, as well as a C-terminal SPASM domain that contains two auxiliary [4Fe-4S] clusters. Importantly, one [4Fe-4S] cluster in the SPASM domain exhibits an open coordination site in absence of peptide substrate, which is coordinated by a peptidyl-cysteine residue in the bound state. The crystal structure of CteB also reveals an accessory N-terminal domain that has high structural similarity to a recently discovered motif present in several enzymes that act on ribosomally synthesized and post-translationally modified peptides (RiPPs), known as a RiPP precursor peptide recognition element (RRE). This crystal structure is the first of a sactionine bond forming enzyme and sheds light on structures and mechanisms of other members of this class such as AlbA or ThnB

The PHENIX Experiment at RHIC

The physics emphases of the PHENIX collaboration and the design and current status of the PHENIX detector are discussed. The plan of the collaboration for making the most effective use of the available luminosity in the first years of RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program available at http://www.rhic.bnl.gov/phenix

Railroad-Highway Grade Crossing Signal Visibility Improvement Program, Volume I: Final Report

DTFH61-84-30027This report documents the methodology, developments, and findings of the two-year study. Among the significant results of this project are: (1) a new set of crossing signal visibility specifications based on widely accepted definitions of motorists' requirements and a demonstration that currently available signals exceed these specifications when properly maintained; (2) the evaluation of seven alterations to standard crossing signal design and operation with respect to performance improvement and maintenance requirements--several of these modifications offer attractive cost/benefit attributes and are recommended for implementation; and (3) the development and evaluation of three tools of potential value to signal maintenance crews: an alignment scope to aid in aiming of the signal for maximum effectiveness, a signal focusing tool to aid in the critical positioning of the signal lamp with respect to the reflector, and a signal flux meter for measuring the light output of crossing and traffic signals--all of these tools were proven effective and would be useful to a conscientious maintenance team. The prototype signal hardware underwent rigorous laboratory, environmental, and field tests. The maintenance tools were evaluated under laboratory conditions