Purification and characterization of a novel extracellular tripeptidyl peptidase from Rhizopus oligosporus

Molecular profiling of sponge deflation reveals an ancient relaxant-inflammatory response

A hallmark of animals is the coordination of whole-body movement. Neurons and muscles are central to this, yet coordinated movements also exist in sponges that lack these cell types. Sponges are sessile animals with a complex canal system for filter-feeding. They undergo whole-body movements resembling "contractions" that lead to canal closure and water expulsion. Here, we combine 3D optical coherence microscopy, pharmacology, and functional proteomics to elucidate anatomy, molecular physiology, and control of these movements. We find them driven by the relaxation of actomyosin stress fibers in epithelial canal cells, which leads to whole-body deflation via collapse of the incurrent and expansion of the excurrent system, controlled by an Akt/NO/PKG/A pathway. A concomitant increase in reactive oxygen species and secretion of proteinases and cytokines indicate an inflammation-like state reminiscent of vascular endothelial cells experiencing oscillatory shear stress. This suggests an ancient relaxant-inflammatory response of perturbed fluid-carrying systems in animals.

Evaluation of the milk clotting properties of an aspartic peptidase secreted by Rhizopus microsporus

Traditionally, chymosin has been used for milk-clotting, but this naturally occurring enzyme is in short supply and its use has raised religious and ethical concerns. Because milk-clotting peptidases are a promising substitute for chymosin in cheese preparation, there is a need to find and test the specificity of these enzymes. Here, we evaluated the milk-clotting properties of an aspartic peptidase secreted by Rhizopus microsporus. The molecular mass of this enzyme was estimated at 36 kDa and Pepstatin A was determined to be an inhibitor. Optimal activity occurred at a pH of 5.5 and a temperature range of 50-60 °C, but the peptidase was stable in the pH range of 4-7 and a temperature as low as 45 °C. Proteolytic activity was significantly reduced in the presence of Cu²⁺ and Al³⁺. When enzyme substrates based on FRET were used, this peptidase exhibited the highest catalytic efficiency for Abz-KNRSSKQ-EDDnp (4,644 ± 155 mM^-1.s^-1), Abz-KLRSSNQ-EDDnp (3,514 ± 130 mM^-1.s^-1), and Abz-KLRQSKQ-EDDnp (3,068 ± 386 mM^-1.s^-1). This study presents a promising peptidase for use in cheese making, due to its high stability in the presence of Ca²⁺ and broad pH range of 4-7, in addition to its ability to efficiently clot milk.

Salt Taste Enhancing l-Arginyl Dipeptides from Casein and Lysozyme Released by Peptidases of Basidiomycota

Some l-arginyl dipeptides were recently identified as salt taste enhancers, thus opening the possibility to reduce dietary sodium uptake without compromising palatability. A screening of 15 basidiomycete fungi resulted in the identification of 5 species secreting a high peptidolytic activity (>3 kAU/mL; azocasein assay). PFP-LC-MS/MS and HILIC-MS/MS confirmed that l-arginyl dipeptides were liberated when casein or lysozyme served as substrate. Much higher yields of dipeptides (42-75 μmol/g substrate) were released from lysozyme than from casein. The lysozyme hydrolysate generated by the complex set of peptidases of Trametes versicolor showed the highest l-arginyl dipeptide yields and a significant salt taste enhancing effect in a model cheese matrix and in a curd cheese. With a broad spectrum of novel specific and nonspecific peptidases active in the slightly acidic pH range, T. versicolor might be a suitable enzyme source for low-salt dairy products.