The cofactor arrangement and the mode of binding to the protein seem to be very similar among the non-sulphur bacterial photosynthetic RCs. The functional role of the displaced QB molecule, which might be present as quinol, rather than quinone, is not yet clear. The newly discovered water chain to the QB binding site suggests a pathway for the protonation of the secondary quinone QB.

No abstract

Vinorine synthase is an acetyltransferase that occupies a central role in the biosynthesis of the antiarrhythmic monoterpenoid indole alkaloid ajmaline in the plant Rauvolfia. Vinorine synthase belongs to the benzylalcohol acetyl-, anthocyanin-O-hydroxy-cinnamoyl-, anthranilate-N-hydroxy-cinnamoyl/benzoyl-, deacetylvindoline acetyltransferase (BAHD) enzyme superfamily, members of which are involved in the biosynthesis of several important drugs, such as morphine, Taxol, or vindoline, a precursor of the anti-cancer drugs vincaleucoblastine and vincristine. The x-ray structure of vinorine synthase is described at 2.6-Å resolution. Despite low sequence identity, the two-domain structure of vinorine synthase shows surprising similarity with structures of several CoA-dependent acyltransferases such as dihydrolipoyl transacetylase, polyketide-associated protein A5, and carnitine acetyltransferase. All conserved residues typical for the BAHD family are found in domain 1. His 160 of the HXXXD motif functions as a general base during catalysis. It is located in the center of the reaction channel at the interface of both domains and is accessible from both sides. The channel runs through the entire molecule, allowing the substrate and co-substrate to bind independently. Asp 164 points away from the catalytic site and seems to be of structural rather than catalytic importance. Surprisingly, the DFGWG motif, which is indispensable for the catalyzed reaction and unique to the BAHD family, is located far away from the active site and seems to play only a structural role. Vinorine synthase represents the first solved protein structure of the BAHD superfamily.The acyl-CoA-dependent BAHD 1 superfamily is a fast growing enzyme family that has only recently been defined (1). The name BAHD is coined from the first four enzymes of the family isolated from plant species. The members of this family play an important role in the biosynthesis of a variety of secondary metabolites. The family might become significantly larger in the near future because ϳ70 BAHD-related genes have been identified recently in the Arabidopsis genome (2), and in most cases, their biochemical function still needs to be explored. Several BAHD members occurring in medicinal plants and fungi play very specific metabolic roles in biosynthetic pathways. The most prominent members are, for instance, those participating in the biosynthesis of the Catharanthus alkaloid vindoline (3), a precursor of the anti-cancer drugs vincaleucoblastine and vincristine, the Papaver alkaloid morphine (4), the diterpenoid alkaloid Taxol (5-7), anthocyanins (8 -10) as well as some phytoalexins (11), and enzymes involved in floral scent (12).A well-characterized enzyme of this family is vinorine synthase (VS; EC 2.3.1.160), which is of central importance in the endogenous formation of monoterpenoid indole alkaloids of the ajmalan type in the plant genus Rauvolfia. The synthase is located in the middle of the complex biosynthetic pathway that starts with tryptamine and the monoterpene s...

The crystal structure of the DFPase from Loligo vulgaris is the first example of a structural characterization of a squid-type DFPase and the second crystal structure of a PTE determined to date. Therefore, it may serve as a structural model for squid-type DFPases in general. The overall structure of this protein represents a six-fold beta propeller with two calcium ions bound in a central water-filled tunnel. The consensus motif found in the blades of this beta propeller has not yet been observed in other beta propeller structures. Based on the results obtained from mutants of active-site residues, a mechanistic model for the DFP hydrolysis has been developed.

X-ray structures of the wild-type reaction centre from Rhodobacter sphaeroides have been determined to a resolution of 1.87 Å in the neutral (dark) state and to 2.06 Å in the charge-separated (lightexcited) state. Whereas the overall protein structures of both states are rather similar, the domain around the secondary quinone shows significant shifts. The quinone molecule itself is observed at two different positions. In the neutral state, 55% of the quinone is located distally and 45% proximally to the cytoplasmic side. After excitation by light, however, at least 90% of the quinone is found at the proximal position. Results presented by Stowell et al. (1997) are confirmed, but the quality of crystallographic data has been improved. We compare the data with the structure of the mutant RC L209 PY that keeps the Q B molecule in the proximal position even in the charge-neutral state.