Structural Study of Metal Binding and Coordination in Ancient Metallo-ß-Lactamase PNGM-1 Variants.

The increasing incidence of community- and hospital-acquired infections with multidrug-resistant (MDR) bacteria poses a critical threat to public health and the healthcare system. Although ß-lactam antibiotics are effective against most bacterial infections, some bacteria are resistant to ß-lactam antibiotics by producing ß-lactamases. Among ß-lactamases, metallo-ß-lactamases (MBLs) are especially worrisome as only a few inhibitors have been developed against them. In MBLs, the metal ions play an important role as they coordinate a catalytic water molecule that hydrolyzes ß-lactam rings. We determined the crystal structures of different variants of PNGM-1, an ancient MBL with additional tRNase Z activity. The variants were generated by site-directed mutagenesis targeting metal-coordinating residues. In PNGM-1, both zinc ions are coordinated by six coordination partners in an octahedral geometry, and the zinc-centered octahedrons share a common face. Structures of the PNGM-1 variants confirm that the substitution of a metal-coordinating residue causes the loss of metal binding and ß-lactamase activity. Compared with PNGM-1, subclass B3 MBLs lack one metal-coordinating residue, leading to a shift in the metal-coordination geometry from an octahedral to tetrahedral geometry. Our results imply that a subtle change in the metal-binding site of MBLs can markedly change their metal-coordination geometry and catalytic activity.

Catalytic Intermediate Crystal Structures of Cysteine Desulfurase from the Archaeon Thermococcus onnurineus NA1.

Thermococcus onnurineus NA1 is an anaerobic archaeon usually found in a deep-sea hydrothermal vent area, which can use elemental sulfur (S0) as a terminal electron acceptor for energy. Sulfur, essential to many biomolecules such as sulfur-containing amino acids and cofactors including iron-sulfur cluster, is usually mobilized from cysteine by the pyridoxal 5'-phosphate- (PLP-) dependent enzyme of cysteine desulfurase (CDS). We determined the crystal structures of CDS from Thermococcus onnurineus NA1 (ToCDS), which include native internal aldimine (NAT), gem-diamine (GD) with alanine, internal aldimine structure with existing alanine (IAA), and internal aldimine with persulfide-bound Cys356 (PSF) structures. The catalytic intermediate structures showed the dihedral angle rotation of Schiff-base linkage relative to the PLP pyridine ring. The ToCDS structures were compared with bacterial CDS structures, which will help us to understand the role and catalytic mechanism of ToCDS in the archaeon Thermococcus onnurineus NA1.

Conformational change of organic cofactor PLP is essential for catalysis in PLP-dependent enzymes.

Pyridoxal 5'-phosphate (PLP)-dependent enzymes are ubiquitous, catalyzing various biochemical reactions of approximately 4% of all classified enzymatic activities. They transform amines and amino acids into important metabolites or signaling molecules and are important drug targets in many diseases. In the crystal structures of PLP-dependent enzymes, organic cofactor PLP showed diverse conformations depending on the catalytic step. The conformational change of PLP is essential in the catalytic mechanism. In the study, we review the sophisticated catalytic mechanism of PLP, especially in transaldimination reactions. Most drugs targeting PLP-dependent enzymes make a covalent bond to PLP with the transaldimination reaction. A detailed understanding of organic cofactor PLP will help develop a new drug against PLP-dependent enzymes. [BMB Reports 2022; 55(9): 439-446].

Fructuronate-tagaturonate epimerase UxaE from Cohnella laeviribosi has a versatile TIM-barrel scaffold suitable for a sugar metabolizing biocatalyst.

Xylan and pectin are major structural components of plant cell walls. There are two independent catabolic pathways for xylan and pectin. UxaE bridges these two pathways by reversibly epimerizing D-fructuronate and D-tagaturonate. The crystal structure of UxaE from Cohnella laeviribosi (ClUxaE) shows a core scaffold of TIM-barrel with a position-changing divalent metal cofactor. ClUxaE has the flexible metal-coordination loop to allow the metal shift and the extra domains to bind a phosphate ion in the active site, which are important for catalysis and substrate specificity. Elucidation of the structure and mechanism of ClUxaE will assist in understanding the catalytic mechanism of UxaE family members, which are useful for processing both xylan and pectin-derived carbohydrates for practical and industrial purposes, including the transformation of agricultural wastes into numerous valuable products.

Expression, crystallization and preliminary X-ray crystallographic analysis of cystathionine ß-lyase from Acinetobacter baumannii OXA-23.

Multidrug-resistant Acinetobacter baumannii (Ab) has emerged as a leading nosocomial pathogen because of its resistance to most currently available antibiotics. Cystathionine ß-lyase (CBL), a pyridoxal 5'-phosphate (PLP)-dependent enzyme, catalyzes the second step in the transsulfuration pathway, which is essential for the metabolic interconversion of the sulfur-containing amino acids homocysteine and methionine. The enzymes of the transsulfuration pathway are considered to be attractive drug targets owing to their specificity to microbes and plants. As a potential target for the development of novel antibacterial drugs, the AbCBL protein was expressed, purified and crystallized. An AbCBL crystal diffracted to 1.57 Šresolution and belonged to the trigonal space group P3112, with unit-cell parameters a = b = 102.9, c = 136.5 Å. The asymmetric unit contained two monomers, with a corresponding VM of 2.3 Å(3) Da(-1) and a solvent content of 46.9%.