Acta crystallographica. Section F, Structural biology communications最新文献

The focused issue on the SAMPREP workshop is introduced. The virtual issue is available at https://journals.iucr.org/special_issues/2025/samprep23/.

The enzyme d-aspartate oxidase (DDO) oxidizes acidic d-amino acids using the coenzyme flavin adenine dinucleotide to generate the corresponding α-keto acids and ammonia. DDO differs from d-amino-acid oxidase (DAAO), which acts on neutral and basic d-amino acids. Although the enzymatic properties of DDO have been characterized in several species, the structure of DDO had remained unclear. The structure of DDO derived from Cryptococcus humicola strain UJ1 (chDDO) was determined by X-ray crystallography at 1.70 Å resolution. While the three-dimensional structures of DAAOs are known to be homodimers, chDDO forms a homotetramer. This difference was found to be caused by the deletion of one loop and the insertion of two loops.

Bacillus subtilis DegQ is a 46-amino-acid regulatory protein involved in the DegS–DegU two-component system. DegQ promotes the phosphorylation of DegU by DegS, switching the function of DegU from competence to the induction of poly-γ-glutamate production. To elucidate its structural role, we determined the crystal structures of wild-type DegQ and its mutant DegQS25L. Each DegQ monomer folds into a single α-helix, and four monomers assemble into a tetramer characterized by a four-helix coiled-coil structure. Within the tetramer, two adjacent helices are oriented in the same direction, while the other two are oriented oppositely, forming a pseudo-twofold symmetric arrangement. The mutant form displays disrupted symmetry due to altered helix packing, which is caused by shifts in the coiled-coil heptad register induced by the mutation. Structural predictions using AlphaFold3 suggest that DegQ likely binds to the N-terminal helix bundle of DegS, either as a dimer or as individual monomers. These findings provide structural insight into DegQ oligomerization and its potential role in modulating DegS autophosphorylation and DegU binding.

Several cyanobacterial species, including Crocosphaera subtropica ATCC 51142, accumulate cyanobacterial starch instead of glycogen, although nearly all cyanobacteria accumulate glycogen. The glycogen-producing Synechococcus elongatus PCC 7942 possesses one α-glucan phosphorylase (Pho) isozyme, whereas strain 51142 has three Pho isozymes. Based on their primary structures, these enzymes belong to glycosyl transferase (GT) family 35, with the cyanobacterial GT35-type Phos further subdivided into types I–III. In this study, to elucidate the significance of the coexistence of multiple GT35-type Pho isozymes, those from strain 51142 (type I, cce_1629; type II, cce_1603 and cce_5186) and strain 7942 (type I, Synpcc7942_0244) were overexpressed in Escherichia coli and biochemically characterized. All isozymes catalysed the phosphorolysis and reverse phosphorolysis reactions. The type I isozyme from a cyanobacterial starch-producing strain (cce_1629) differed in substrate specificity and specific activity compared with the others. The behaviour towards the effectors (AMP and ATP) of the type I and type II isozymes differed from each other. These findings enhance our understanding of the roles of cyanobacterial Pho isozymes in α-glucan metabolism. Furthermore, recombinant cce_1603 was crystallized using the hanging-drop vapour-diffusion method. Crystals were obtained at 293 K in the presence of 10 mM maltoheptaose, 45%(w/v) PEG 400, 0.1 M Tris–HCl pH 8.0, 0.2 M lithium sulfate. The crystals belonged to space group R32 (hexagonal setting) with unit-cell parameters a = b = 267.23, c = 204.43 Å, and diffracted to beyond 2.70 Å resolution. Matthews coefficient calculations indicated the presence of two molecules in the asymmetric unit. Structural determination is currently under way. The crystal structure of cce_1603 will aid in the understanding of the structural basis of cyanobacterial GT35-type Pho isozymes.

Gasdermin D (GSDMD) is a protein that has gained significant attention in recent years due to its crucial role in inflammatory cell death, particularly pyroptosis. Pyroptosis is a highly inflammatory form of programmed cell death that is triggered by various microbial infections and sterile inflammatory stimuli. GSDMD acts as an executioner molecule in this process, leading to the release of pro-inflammatory cytokines and amplifying the immune response. Here, we present a higher resolution, significantly improved apo crystal structure of the deposited mouse structure model that will be beneficial for structure-based drug-design approaches towards this important pharmacological target.

The MRE11-RAD50-NBS1/Xrs2 (MRN/X) protein complex acts as a first responder in DNA double-strand break repair and telomere-length maintenance, yet the structural architecture of the yeast ortholog Xrs2 has remained unresolved. In this study, we present the first structure of the folded N-terminal region of Xrs2 from Saccharomyces cerevisiae, resolved at 2.38 Å using X-ray crystallography. Like the previously determined crystal structures of Schizosaccharomyces pombe Nbs1, the folded structure of S. cerevisiae Xrs2 adopts an extended three-domain organization at its N-terminus. Electrostatic analysis reveals two distinct charged patches: a positively charged patch on the FHA domain and a negatively charged patch in the cleft between the FHA and BRCT1 domains. This charge segregation is likely to play a role in mediating interactions with various ligands.