Motivation: Prediction of ligand binding sites of proteins is significant as it can provide insight into biological functions and reaction mechanisms of proteins. It is also a prerequisite for protein–ligand docking and an important step in structure-based drug design. Results: We present a new algorithm, Roll, implemented in a program named POCASA, which can predict binding sites by detecting pockets and cavities of proteins with a rolling sphere. To evaluate the performance of POCASA, a test with the same data set as used in several existing methods was carried out. POCASA achieved a high success rate of 77%. In addition, the test results indicated that POCASA can predict good shapes of ligand binding sites. Availability:A web version of POCASA is freely available at http://altair.sci.hokudai.ac.jp/g6/Research/POCASA_e.html Contact:yao@castor.sci.hokudai.ac.jp Supplementary information: Supplementary data are available at Bioinformatics online.

The cellulose synthesizing terminal complex consisting of subunits A, B, C, and D in Acetobacter xylinum spans the outer and inner cell membranes to synthesize and extrude glucan chains, which are assembled into subelementary fibrils and further into a ribbon. We determined the structures of subunit D (AxCeSD/AxBcsD) with both N- and C-terminal His ₆ tags, and in complex with cellopentaose. The structure of AxCeSD shows an exquisite cylinder shape (height: ∼65 Å , outer diameter: ∼90 Å , and inner diameter: ∼25 Å ) with a right-hand twisted dimer interface on the cylinder wall, formed by octamer as a functional unit. All N termini of the octamer are positioned inside the AxCeSD cylinder and create four passageways. The location of cellopentaoses in the complex structure suggests that four glucan chains are extruded individually through their own passageway along the dimer interface in a twisted manner. The complex structure also shows that the N-terminal loop, especially residue Lys6, seems to be important for cellulose production, as confirmed by in vivo assay using mutant cells with axcesD gene disruption and N-terminus truncation. Taking all results together, a model of the bacterial terminal complex is discussed.

SusB, an 84-kDa α-glucoside hydrolase involved in the starch utilization system (sus) of Bacteroides thetaiotaomicron, belongs to glycoside hydrolase (GH) family 97. We have determined the enzymatic characteristics and the crystal structures in free and acarbose-bound form at 1.6Å resolution. SusB hydrolyzes the α-glucosidic linkage, with inversion of anomeric configuration liberating the β-anomer of glucose as the reaction product. The substrate specificity of SusB, hydrolyzing not only α-1,4-glucosidic linkages but also α-1,6-, α-1,3-, and α-1,2-glucosidic linkages, is clearly different from other well known glucoamylases belonging to GH15. The structure of SusB was solved by the single-wavelength anomalous diffraction method with sulfur atoms as anomalous scatterers using an in-house x-ray source. SusB includes three domains as follows: the N-terminal, catalytic, and C-terminal domains. The structure of the SusB-acarbose complex shows a constellation of carboxyl groups at the catalytic center; Glu⁵³² is positioned to provide protonic assistance to leaving group departure, with Glu⁴³⁹ and Glu⁵⁰⁸ both positioned to provide base-catalyzed assistance for inverting nucleophilic attack by water. A structural comparison with other glycoside hydrolases revealed significant similarity between the catalytic domain of SusB and those of α-retaining glycoside hydrolases belonging to GH27, -36, and -31 despite the differences in catalytic mechanism. SusB and the other retaining enzymes appear to have diverged from a common ancestor and individually acquired the functional carboxyl groups during the process of evolution. Furthermore, sequence comparison of the active site based on the structure of SusB indicated that GH97 included both retaining and inverting enzymes.

Proteins Rpf2 and Rrs1 are required for 60S ribosomal subunit maturation. These proteins are necessary for the recruitment of three ribosomal components (5S ribosomal RNA [rRNA], RpL5 and RpL11) to the 90S ribosome precursor and subsequent 27SB pre-rRNA processing. Here we present the crystal structure of the Aspergillus nidulans (An) Rpf2-Rrs1 core complex. The core complex contains the tightly interlocked N-terminal domains of Rpf2 and Rrs1. The Rpf2 N-terminal domain includes a Brix domain characterized by similar N- and C-terminal architecture. The long α-helix of Rrs1 joins the C-terminal half of the Brix domain as if it were part of a single molecule. The conserved proline-rich linker connecting the N- and C-terminal domains of Rrs1 wrap around the side of Rpf2 and anchor the C-terminal domain of Rrs1 to a specific site on Rpf2. In addition, gel shift analysis revealed that the Rpf2-Rrs1 complex binds directly to 5S rRNA. Further analysis of Rpf2-Rrs1 mutants demonstrated that Saccharomyces cerevisiae Rpf2 R236 (corresponds to R238 of AnRpf2) plays a significant role in this binding. Based on these studies and previous reports, we have proposed a model for ribosomal component recruitment to the 90S ribosome precursor.