Recent Insights Into the Prognostic and Therapeutic Applications of Lysozymes

Abstract

Lysozymes are naturally occurring enzymes present in a variety of biological organisms, such as bacteria, fungi, and animal bodily secretions and tissues. It is also the main ingredient of many ethnomedicines. It is well known that lysozymes and lysozyme-like enzymes can be used as anti-bacterial agents by degrading bacterial cell wall peptidoglycan that leads to cell death, and can also inhibit fungi, yeasts, and viruses. In addition to its direct antimicrobial activity, lysozyme is also an important component of the innate immune system in most mammals. Increasing evidence has shown the immune-modulatory effects of lysozymes against infection and inflammation. More recently, studies have revealed the anti-cancer activities of lysozyme in multiple types of tumors, potentially through its immune-modulatory activities. In this review, we summarized the major functions and underlying mechanisms of lysozymes derived from animal and plant sources. We highlighted the therapeutic applications and recent advances of lysozymes in cancers, hypertension, and viral diseases, aiming toseeking alternative therapies for standard medical treatment bypassing side effects. We also evaluated the role of lysozyme as a promising cancer marker for prognosis to indicate the outcomes recurrence for patients.

Keywords: cancer; hypertension; lysozyme; prognosis; therapy; viral disease.

FIGURE 1

Chemical structure simulation diagram of hydrolysis site of lysozyme. The active site of lysozyme is bound to six continuous sugar monomers through six subsites (A-F), and then hydrolyzed by double substitution reaction β- 1,4 glycosidic bond, the catalytic group acts on the D site (A). D and E are stretched into a half chair transition state, the catalytic group glutamic acid (Glu) 35 is bound to the D site, and aspartic acid (Asp) 52 is bound to the E site to hydrolyze the peptidoglycan skeleton of bacterial cell wall (B).

FIGURE 2

Lysozyme is antibacterial through these two mechanisms. The peptidoglycan(PG) skeleton of bacterial cell wall is connected by NAG and NAM through peptide stem, and then anchored on the cell membrane (purple) through lipid carrier. Lysozyme (golden yellow) hydrolyzes the interaction between NAG and NAM on PG β‐ 1,4 glycosidic bonds, leading to bacterial cell wall instability and bacterial death. Secondly, lysozyme (golden yellow) can form pores on negatively charged cell membrane by using its own cation mechanism to achieve sterilization.