and discussion 3. Matthews co-efficient of 2.83??3?Da?1 (i.e. three icosahedral half-molecules; find Fig. 3 ? a). Each BaLS RU 24969 hemisuccinate manufacture molecule includes 60 identical proteins subunits organized in 12 pentamers relative to icosahedral 532 symmetry (Figs. 3 ? b and 3 ? c). The BaLS monomer can be made up of 153 proteins and shows the typical α/β/α-sandwich topology of known LS orthologues. The core of the RU 24969 hemisuccinate manufacture protein subunit is formed by a four-stranded parallel β–sheet which is flanked by α-helices (Fig. 3 ? c). Sequence (Fig. 2 ?) and structural comparisons of the BaLS subunit with icosahedral orthologues showed a very high similarity for secondary-structure elements and only small differences in the conformations of the loops connecting β–strands and α-helices (Fig. 3 ? d). On the other hand comparison of the BaLS subunit with pentameric (non-icosahedral) LSs (Fig. 3 ? e) revealed more distinct differences in RU 24969 hemisuccinate manufacture the loop regions although the secondary-structure elements appeared to be rather conserved between icosahedral and pentameric enzymes. The symmetry-related α3 helices of each pentameric ensemble of icosahedral BaLS surround a central channel. The central part of the channel wall is formed by the side chains of five Lys97 residues creating a positively charged patch whose charge is compensated by the side chains of Glu94. The channel entrances are formed by the polar residues Asp89 and Asn93 and by Gln105 and Glu118 which face the solvent space and the particle core space respectively. The amino-acid side chains inside the channel participate in stabilizing hydrogen-bond interactions. While the solvent content of the BaLS crystals could not be analyzed in detail water molecules have been observed inside the homologous channels of other LS orthologues. The N-terminus of each subunit forms an extra β-strand extending to the β-sheet of the adjacent subunit. 12 pentameric blocks make up one icosahedral particle with a diameter of about 157?? which is rather similar to the previously determined sizes of icosahedral LSs [160?? for LS from S. oleracea (Persson et al. 1999 ?) 154 for LS from A. aeolicus (Zhang et al. 2001 ?) and 156?? for LS from B. subtilis (Ritsert et al. 1995 ?)]. The characteristic icosahedral ionic contacts described at length by Zhang et al. (2001 ?) are well conserved in the BaLS framework although there is certainly one fewer favorably billed Arg residue weighed against LS through the hyperthermophilic bacterium A. aeolicus. The residues mixed up in ionic interactions are VEGFD Arg20 Arg39 Glu23 Glu144 and Asp35. The threefold connections are shaped by residues from helices α1 and α4. This get in touch with can be well conserved in RU 24969 hemisuccinate manufacture every known icosahedral LSs and it is maintained with the hydrogen-bond network of three symmetry-equivalent Lys28 residues from neighbouring subunits on the top of capsid by hydrophobic connections concerning Phe24 Ile120 and Ile124 and by three adversely billed Glu121 residues in the internal surface area from the capsid. The twofold icosahedral axes on the user interface between two pentamers are encircled by residues from the finish of strand β4 as well as the loop hooking up helices α4 and α5. The connections between pairs of adjacent subunits in the pentamer have become intensive. 3.3 Dynamic site The cavities formed on the subunit interfaces will be the energetic sites of lumazine synthase where both substrates (i.e. com-pounds 1 and 2; Fig. 1 ?are bound ). All icosahedral LSs including BaLS possess 60 equal energetic sites notably. The heteroaromatic band systems of substance 1 or substrate-analogous inhibitors can be found within a hydrophobic pocket. Their ribityl aspect string is certainly embedded within a surface area depression which is certainly less available RU 24969 hemisuccinate manufacture to solvent compared to the band system as well as the alkylphos-phonyl or alkylphosphate string. The binding of substrate-analogous inhibitors to LS seems to follow an induced-fit system the following. The phenyl band of Phe20 swings into an orientation parallel towards the heteroaromatic band program of the inhibitors (π-π relationship).