Decoding the Structure-Function Relationship of the Muramidase Domain in E. coli O157.H7 Bacteriophage Endolysin: A Potential Building Block for Chimeric Enzybiotics.

Bacteriophage endolysins are potential alternatives to conventional antibiotics for treating multidrug-resistant gram-negative bacterial infections. However, their structure-function relationships are poorly understood, hindering their optimization and application. In this study, we focused on the individual functionality of the C-terminal muramidase domain of Gp127, a modular endolysin from E. coli O157:H7 bacteriophage PhaxI. This domain is responsible for the enzymatic activity, whereas the N-terminal domain binds to the bacterial cell wall. Through protein modeling, docking experiments, and molecular dynamics simulations, we investigated the activity, stability, and interactions of the isolated C-terminal domain with its ligand. We also assessed its expression, solubility, toxicity, and lytic activity using the experimental data. Our results revealed that the C-terminal domain exhibits high activity and toxicity when tested individually, and its expression is regulated in different hosts to prevent self-destruction. Furthermore, we validated the muralytic activity of the purified refolded protein by zymography and standardized assays. These findings challenge the need for the N-terminal binding domain to arrange the active site and adjust the gap between crucial residues for peptidoglycan cleavage. Our study shed light on the three-dimensional structure and functionality of muramidase endolysins, thereby enriching the existing knowledge pool and laying a foundation for accurate in silico modeling and the informed design of next-generation enzybiotic treatments.

Baeyer-Villiger oxidation of progesterone by Aspergillus sojae PTCC 5196.

Microbial transformations are capable of producing steroid substances difficult to synthesize by chemical methods. Strains belonging to the genus Aspergillus are effective facilitators of microbial biotransformations due to their enzymatic diversity. In this study, the biotransformation of progesterone by the fungus Aspergillus sojae (A. sojae) PTCC 5196 was examined. Analysis of the bioconversion process revealed that progesterone was converted to testololactone through a three-step pathway (17ß-acetyl side chain cleavage, 17ß-hydroxyl oxidation, and oxygenative lactonization of 17-ketone), indicating the presence of Baeyer-Villiger monooxygenase (BVMO) activity in the fungal strain. GC analysis confirmed the production of testololactone with a yield of 99% in 24 h. Faster testololactone production was induced in the presence of both C-21 (progesterone) and C-19 (androstenedione, testosterone, and dehydroepiandrosterone [DHEA]) steroid substances. Due to the high biotransformation rate observed in the present study, A. sojae may be a novel and promising candidate in the production of testololactone.