Structural and Biochemical Features of OXA-517: a Carbapenem and Expanded-Spectrum Cephalosporin Hydrolyzing OXA-48 Variant.

OXA-48-producing Enterobacterales have now widely disseminated throughout the world. Several variants have now been reported, differing by just a few amino-acid substitutions or deletions, mostly in the region of the loop β5-β6. As OXA-48 hydrolyzes carbapenems but lacks significant expanded-spectrum cephalosporin (ESC) hydrolytic activity, ESCs were suggested as a therapeutic option.

Flexible loops of New Delhi metallo-β-lactamase modulate its activity towards different substrates.

Two accessory loop regions that are present in numerous variants of New Delhi metallo-β-lactamases (NDM) are important for the enzymatic activity. The first one is a flexible loop L3 that is located near the active site and is thought to play an important role in the catalytic process. The second region, Ω loop is located close to a structural element that coordinates two essential zinc ions.

Structural Insight into DNA-Dependent Activation of Human Metalloprotease Spartan.

The DNA-dependent metalloprotease Spartan (SPRTN) cleaves DNA-protein crosslinks (DPCs) and protects cells from DPC-induced genome instability. Germline mutations of SPRTN are linked to human Ruijs-Aalfs syndrome (RJALS) characterized by progeria and early-onset hepatocellular carcinoma. The mechanism of DNA-mediated activation of SPRTN is not understood.

A close look onto structural models and primary ligands of metallo-β-lactamases.

β-Lactamases are hydrolytic enzymes capable of opening the β-lactam ring of antibiotics such as penicillin, thus endowing the bacteria that produce them with antibiotic resistance. Of particular medical concern are metallo-β-lactamases (MBLs), with an active site built around coordinated Zn cations. MBLs are pan-reactive enzymes that can break down almost all classes of β-lactams, including such last-resort antibiotics as carbapenems.

Prior knowledge or freedom of interpretation? A critical look at a recently published classification of "novel" Zn binding sites.

In a recently published article (Yao, Flight, Rouchka, and Moseley, Proteins 2015;83:1470-1487) the authors proposed novel Zn coordination patterns in protein structures, apparently discovered using an unprejudiced approach to the information collected in the Protein data Bank (PDB), which they advocated as superior to the prior-knowledge-informed paradigm. In our assessment of those propositions we demonstrate here that most, if not all, of the "new" coordination geometries are fictitious, as they are based on incorrectly interpreted protein crystal structures, which in themselves are often not error-free. The flaws of interpretation include partial or wrong Zn sites, missed or wrong ligands, ignored crystal symmetry and ligands, etc.

Structure of a complete four-domain chitinase from Moritella marina, a marine psychrophilic bacterium.

X-ray crystallography reveals chitinase from the psychrophilic bacterium Moritella marina to be an elongated molecule which in addition to the catalytic β/α-barrel domain contains two Ig-like domains and a chitin-binding domain, all linked in a chain. A ligand-binding study using NAG oligomers showed the enzyme to be active in the crystal lattice and resulted in complexes of the protein with oxazolinium ion (the reaction intermediate) and with NAG2, a reaction product. The characteristic motif DXDXE, containing three acidic amino-acid residues, which is a signature of type 18 chitinases, is conserved in the enzyme.

Crystallographic analysis of a thermoactive nitrilase.

The nitrilase superfamily is a large and diverse superfamily of enzymes that catalyse the cleavage of various types of carbon-nitrogen bonds using a Cys-Glu-Lys catalytic triad. Thermoactive nitrilase from Pyrococcus abyssi (PaNit) hydrolyses small aliphatic nitriles like fumaro- and malononitryl. Yet, the biological role of this enzyme is unknown.