Mytilus chilensis is considered an important food source for the Chilean population and represents a considerable fraction of its aquacultural production, mainly in southern Chile’s coastal regions. This study aimed to assess the concentrations of total arsenic (tAs), lead (Pb), and cadmium (Cd), their bioaccessibility, and associated health risks in M. chilensis from the Valdivia River Estuary (VRE) in the Los Ríos Region and the Reloncaví Fjord (RF) in the Los Lagos Region. The metal concentrations were quantified using Inductively Coupled Plasma–Optical Emission Spectrometry (ICP-OES). The concentrations of tAs, Cd, and Pb were 6682 ± 2018, 1592 ± 742, and 1208 ± 639 ng/g d.w., respectively. Variations in the metal concentrations were observed across areas, months, and sampling points but remained below national and international limits. No correlation was found between the metal concentrations and environmental parameters. The bioaccessibility percentages were tAs (68 ± 10%), Cd (45 ± 21%), and Pb (15 ± 4%). The tAs, Pb and Cd levels in M. chilensis from southern Chile do not represent a risk to human health.

Endoxylanases belonging to family 10 of the glycoside hydrolases (GH10) are versatile in the use of different substrates. Thus, an understanding of the molecular mechanisms underlying substrate specificities could be very useful in the engineering of GH10 endoxylanases for biotechnological purposes. Herein, we analyzed XynA, an endoxylanase that contains a (β/α)₈-barrel domain and an intrinsically disordered region (IDR) of 29 amino acids at its amino end. Enzyme activity assays revealed that the elimination of the IDR resulted in a mutant enzyme (XynAΔ29) in which two new activities emerged: the ability to release xylose from xylan, and the ability to hydrolyze p-nitrophenyl-β-d-xylopyranoside (pNPXyl), a substrate that wild-type enzyme cannot hydrolyze. Circular dichroism and tryptophan fluorescence quenching by acrylamide showed changes in secondary structure and increased flexibility of XynAΔ29. Molecular dynamics simulations revealed that the emergence of the pNPXyl-hydrolyzing activity correlated with a dynamic behavior not previously observed in GH10 endoxylanases: a hinge-bending motion of two symmetric regions within the (β/α)₈-barrel domain, whose hinge point is the active cleft. The hinge-bending motion is more intense in XynAΔ29 than in XynA and promotes the formation of a wider active site that allows the accommodation and hydrolysis of pNPXyl. Our results open new avenues for the study of the relationship between IDRs, dynamics and activity of endoxylanases, and other enzymes containing (β/α)₈-barrel domain.