Crystal structure and inhibition studies of transglutaminase from Streptomyces mobaraense.

The crystal structure of the microbial transglutaminase (MTGase) zymogen from Streptomyces mobaraense has been determined at 1.9-Å resolution using the molecular replacement method based on the crystal structure of the mature MTGase. The overall structure of this zymogen is similar to that of the mature form, consisting of a single disk-like domain with a deep active cleft at the edge of the molecule. A major portion of the prosequence (45 additional amino acid residues at the N terminus of the mature transglutaminase) folds into an L-shaped structure, consisting of an extended N-terminal segment linked with a one-turn short helix and a long α-helix. Two key residues in the short helix of the prosequence, Tyr-12 and Tyr-16, are located on top of the catalytic triad (Cys-110, Asp-301, and His-320) to block access of the substrate acyl donors and acceptors. Biochemical characterization of the mature MTGase, using N-α-benzyloxycarbonyl-L-glutaminylglycine as a substrate, revealed apparent K(m) and k(cat)/K(m) values of 52.66 mM and 40.42 mM(-1) min(-1), respectively. Inhibition studies using the partial prosequence SYAETYR and homologous sequence SQAETYR showed a noncompetitive inhibition mechanism with IC(50) values of 0.75 and 0.65 mM, respectively, but no cross-linking product formation. Nevertheless, the prosequence homologous oligopeptide SQAETQR, with Tyr-12 and Tyr-16 each replaced with Gln, exhibited inhibitory activity with the formation of the SQAETQR-monodansylcadaverine fluorophore cross-linking product (SQAETQR-C-DNS). MALDI-TOF tandem MS analysis of SQAETQR-C-DNS revealed molecular masses corresponding to those of (N)SQAETQ(C)-C-DNS and C-DNS-(N)QR(C) sequences, suggesting the incorporation of C-DNS onto the C-terminal Gln residue of the prosequence homologous oligopeptide. These results support the putative functional roles of both Tyr residues in substrate binding and inhibition.

Crystallization and preliminary crystallographic study of the phosphoglucose isomerase from Bacillus subtilis.

Crystallization and preliminary crystallographic analysis of the phosphoglucose isomerase from a Bacillus subtilis native strain were carried out. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 145.7, b = 136.0, c = 109.1 A, beta = 119.4 degrees . The diffraction quality of the crystal was significantly improved from 2.4 A to greater than 1.9 A resolution by using the in situ flash-annealing method. A 98% complete data set with an overall R(merge) of 4.6% was collected using an R-AXIS IV(++) image-plate system and a copper rotating-anode X-ray generator. The crystals contained four molecules per asymmetric unit and the predicted solvent content and the Matthews coefficient (V(M)) were 46.8% and 2.3 A(3) Da(-1), respectively. Structure determination by the molecular-replacement method provided a reasonable solution for model building.

The 1.5 A structure of endo-1,3-beta-glucanase from Streptomyces sioyaensis: evolution of the active-site structure for 1,3-beta-glucan-binding specificity and hydrolysis.

The catalytic domain structure of Streptomyces sioyaensis 1,3-beta-glucanase (278 amino acids), a member of glycosyl hydrolase family 16 (GHF16), was determined to 1.5 A resolution in space group P2(1)2(1)2(1). The enzyme specifically hydrolyzes the glycosidic bond of the 1,3-beta-linked glucan substrate. The overall structure contains two antiparallel six-and seven-stranded beta-sheets stacked in a beta-sandwich jelly-roll motif similar to the fold of GHF16 1,3-1,4-beta-glucanases. The active-site cleft of the enzyme is distinct, with the closure of one end primarily caused by two protruding loop insertions and two key residues, Tyr38 and Tyr134. The current known structures of 1,3-1,4-beta-glucanases and 1,3-beta-glucanase from Nocardiopsis sp., on the other hand, have open-channel active-site clefts that can accommodate six beta-D-glucopyranosyl units. The active-site structure of 1,3-beta-glucanase was compared with those of other homologous structures in order to address the binding and enzymatic specificity for 1,3-beta-linked glucans in Streptomyces. This information could be helpful in the development of specific antifungal agents.