Crystallographic fragment screening-based study of a novel FAD-dependent oxidoreductase from Chaetomium thermophilum. Corrigendum.

The synchrotron facilities used in collecting the data for the article by Svecová et al. [(2021), Acta Cryst. D77, 755-775] are acknowledged.

Crystallographic fragment screening-based study of a novel FAD-dependent oxidoreductase from Chaetomium thermophilum.

The FAD-dependent oxidoreductase from Chaetomium thermophilum (CtFDO) is a novel thermostable glycoprotein from the glucose-methanol-choline (GMC) oxidoreductase superfamily. However, CtFDO shows no activity toward the typical substrates of the family and high-throughput screening with around 1000 compounds did not yield any strongly reacting substrate. Therefore, protein crystallography, including crystallographic fragment screening, with 42 fragments and 37 other compounds was used to describe the ligand-binding sites of CtFDO and to characterize the nature of its substrate. The structure of CtFDO reveals an unusually wide-open solvent-accessible active-site pocket with a unique His-Ser amino-acid pair putatively involved in enzyme catalysis. A series of six crystal structures of CtFDO complexes revealed five different subsites for the binding of aryl moieties inside the active-site pocket and conformational flexibility of the interacting amino acids when adapting to a particular ligand. The protein is capable of binding complex polyaromatic substrates of molecular weight greater than 500 Da.

A muramidase from Acremonium alcalophilum hydrolyse peptidoglycan found in the gastrointestinal tract of broiler chickens.

This study evaluates peptidoglycan hydrolysis by a microbial muramidase from the fungus Acremonium alcalophilum in vitro and in the gastrointestinal tract of broiler chickens. Peptidoglycan used for in vitro studies was derived from 5 gram-positive chicken gut isolate type strains. In vitro peptidoglycan hydrolysis was studied by three approaches: (a) helium ion microscopy to identify visual phenotypes of hydrolysis, (b) reducing end assay to quantify solubilization of peptidoglycan fragments, and (c) mass spectroscopy to estimate relative abundances of soluble substrates and reaction products. Visual effects of peptidoglycan hydrolysis could be observed by helium ion microscopy and the increase in abundance of soluble peptidoglycan due to hydrolysis was quantified by a reducing end assay. Mass spectroscopy confirmed the release of hydrolysis products and identified muropeptides from the five different peptidoglycan sources. Peptidoglycan hydrolysis in chicken crop, jejunum, and caecum samples was measured by quantifying the total and soluble muramic acid content. A significant increase in the proportion of the soluble muramic acid was observed in all three segments upon inclusion of the microbial muramidase in the diet.

Structure of a dimeric fungal α-type carbonic anhydrase.

The crystal structure of Aspergillus oryzae carbonic anhydrase (AoCA) was determined at 2.7Å resolution and it revealed a dimer, which only has precedents in the α class in two membrane and cancer-associated enzymes. α carbonic anhydrases are underrepresented in fungi compared to the ß class, this being the first structural representative. The overall fold and zinc binding site resemble other well studied carbonic anhydrases. A major difference is that the histidine, thought to be the major proton shuttle residue in most mammalian enzymes, is replaced by a phenylalanine in AoCA. This finding poses intriguing questions as to the biological functions of fungal α carbonic anhydrases, which are promising candidates for biotechnological applications.