Effects of Conversion of the Zinc-Binding Motif Sequence of Thermolysin, HEXXH, to That of Dipeptidyl Peptidase III, HEXXXH, on the Activity and Stability of Thermolysin

Insights into the Chemistry, Structure, and Biological Activity of Human Salivary MUC7 Fragments and Their Cu(II) and Zn(II) Complexes

Mucin 7 (MUC7) is one of the salivary proteins whose role in the innate immune system is widely known, but still, neither its mechanism of action nor the impact of its metal coordination is fully understood. MUC7 and its fragments demonstrate potent antimicrobial activity, serving as a natural defense mechanism for organisms against pathogens. This study delves into the bioinorganic chemistry of MUC7 fragments (L1─EGRERDHELRHRRHHHQSPK; L2─EGRERDHELRHRR; L3─HHHQSPK) and their complexes with Cu(II) and Zn(II) ions. The antimicrobial characteristics of the investigated peptides and their complexes were systematically assessed against bacterial and fungal strains at pH 5.40 and pH 7.40. Our findings highlight the efficacy of these systems against Streptococcus sanguinis, a common oral cavity pathogen. Most interestingly, Zn(II) coordination increased (or triggered) the MUC7 antimicrobial activity, which underscores the pivotal role of metal ion coordination in governing the antimicrobial activity of human salivary MUC7 fragments against S. sanguinis.

An angiotensin converting enzyme homolog is required for volatile pheromone detection, odorant binding protein secretion and normal courtship behavior in Drosophila melanogaster

In many arthropods, including insects responsible for transmission of human diseases, behaviors that include mating, aggregation, and aggression are triggered by detection of pheromones. Extracellular odorant binding proteins are critical for pheromone detection in many insects and are secreted into the fluid bathing the olfactory neuron dendrites. In Drosophila melanogaster, the odorant binding protein LUSH is essential for normal sensitivity to the volatile sex pheromone, 11-cis vaccenyl acetate (cVA). Using a genetic screen for cVA pheromone insensitivity, we identified ANCE-3, a homolog of human angiotensin converting enzyme that is required for detection of cVA pheromone. The mutants have normal dose-response curves for food odors, although olfactory neuron amplitudes are reduced in all olfactory neurons examined. ance-3 mutants have profound delays in mating, and the courtship defects are primarily but not exclusively due to loss of ance-3 function in males. We demonstrate that ANCE-3 is required in the sensillae support cells for normal reproductive behavior, and that localization of odorant binding proteins to the sensillum lymph is blocked in the mutants. Expression of an ance-3 cDNA in sensillae support cells completely rescues the cVA responses, LUSH localization, and courtship defects. We show the courtship latency defects are not due to effects on olfactory neurons in the antenna nor mediated through ORCO receptors, but instead stem from ANCE-3-dependent effects on chemosensory sensillae in other body parts. These findings reveal an unexpected factor critical for pheromone detection with profound influence on reproductive behaviors.

The specific applications of the TSR-based method in identifying Zn2+ binding sites of proteases and ACE/ACE2

We have developed an alignment-free TSR (Triangular Spatial Relationship)-based computational method for protein structural comparison and motif identification and discovery. To demonstrate the potential applications of the method, we have generated two datasets. One dataset contains five classes: Actin/Hsp70, serine protease (chymotrypsin/trypsin/elastase), ArsC/Prdx2, PKA/PKB/PKC, and AChE/BChE at the hierarchical level 1 and twelve groups at the level 2. The other dataset includes representative proteases and ACE/ACE2. The x,y, z coordinates of the structures were obtained from PDB. We calculated the keys (or features) that represent each structure using the TSR-based method. The dataset and data presented here include additional information that help the readers become aware of specific applications of the TSR-based method in protein clustering, identification and discovery of metal ion binding sites as well as to understand the effect of amino acid grouping on protein 3D structural relationships at both global and local levels.

Enzyme inhibition as a potential therapeutic strategy to treat COVID-19 infection

With the emergence of the third infectious and virulent coronavirus within the past two decades, it has become increasingly important to understand how the virus causes infection. This will inform therapeutic strategies that target vulnerabilities in the vital processes through which the virus enters cells. This review identifies enzymes responsible for SARS-CoV-2 viral entry into cells (ACE2, Furin, TMPRSS2) and discuss compounds proposed to inhibit viral entry with the end goal of treating COVID-19 infection. We argue that TMPRSS2 inhibitors show the most promise in potentially treating COVID-19, in addition to being a pre-existing medication with fewer predicted side-effects.

The extracellular contractile injection system is enriched in environmental microbes and associates with numerous toxins

The extracellular Contractile Injection System (eCIS) is a toxin-delivery particle that evolved from a bacteriophage tail. Four eCISs have previously been shown to mediate interactions between bacteria and their invertebrate hosts. Here, we identify eCIS loci in 1,249 bacterial and archaeal genomes and reveal an enrichment of these loci in environmental microbes and their apparent absence from mammalian pathogens. We show that 13 eCIS-associated toxin genes from diverse microbes can inhibit the growth of bacteria and/or yeast. We identify immunity genes that protect bacteria from self-intoxication, further supporting an antibacterial role for some eCISs. We also identify previously undescribed eCIS core genes, including a conserved eCIS transcriptional regulator. Finally, we present our data through an extensive eCIS repository, termed eCIStem. Our findings support eCIS as a toxin-delivery system that is widespread among environmental prokaryotes and likely mediates antagonistic interactions with eukaryotes and other prokaryotes.

Structural analysis of metal chelation of the metalloproteinase thermolysin by 1,10-phenanthroline

Metalloproteases and their inhibitors are important in numerous fundamental biochemical phenomena and medical applications. The heterocyclic organic compound, 1,10-phenanthroline, forms a complex with transition metal ions and is a Zn²⁺-chelating metalloprotease inhibitor; however, the mechanism of 1,10-phenanthroline-based chelation inhibition has not been fully elucidated. This study aimed to understand the structural basis of zinc metalloproteinase inhibition by 1,10-phenanthroline. Herein, the crystal structure of thermolysin was determined in the absence and presence of 1,10-phenanthroline at 1.5 and 1.8 Å, respectively. In native thermolysin, Zn²⁺ at the active site is tetrahedrally coordinated by His142, His146, Glu166, and water molecule and contains three Ca²⁺ ions, which are involved in thermostability. In the crystal structure of 1,10-phenanthroline-treated thermolysin crystal, seven 1,10-phenanthroline molecules were observed on the surface of thermolysin. These molecules are stabilized by π- π stacking interactions with aromatic amino acids (Phe63, Tyr66, Tyr110, His216, and Try251) or between the 1,10-phenanthrolines. Moreover, interactions with Ser5 and Arg101 were also observed. In this structure, Zn²⁺ at the active site was completely chelated, but no large conformational changes were observed in Zn²⁺ coordination with amino acid residues. Ca²⁺ at the Ca3 site exposed to the solvent was chelated by 1,10-phenanthroline, resulting in a conformational change in the side chain of Asp56 and Gln61. Based on the surface structure, for 1,10-phenanthroline to chelate a metal, it is important that the metal is exposed on the protein surface and that there is no steric hindrance impairing 1,10-phenanthroline access by the amino acids around the metal.