Abstract
Lysozyme is a key effector molecule of the innate immune system in both vertebrate and invertebrate. It is classified into six types, one of which is the goose-type (g-type). To date, no study on g-type lysozyme in crustacean has been documented. Here, we report the identification and characterization of a g-type lysozyme (named LysG1) from the shrimp inhabiting a deep-sea hydrothermal vent in Manus Basin. LysG1 possesses conserved structural features of g-type lysozymes. The recombinant LysG1 (rLysG1) exhibited no muramidase activity and killed selectively Gram-negative bacteria in a manner that depended on temperature, pH, and metal ions. rLysG1 bound target bacteria via interaction with bacterial cell wall components, notably lipopolysaccharide (LPS), and induced cellular membrane permeabilization, which eventually caused cell lysis. The endotoxin-binding capacity enabled rLysG1 to alleviate the inflammatory response induced by LPS. Mutation analysis showed that the bacterial binding and killing activities of rLysG1 required the integrity of the conserved α3 and 4 helixes of the protein. Together, these results provide the first insight into the activity and working mechanism of g-type lysozyme in crustacean and deep-sea organisms.
Highlights
Accepted: 4 December 2021The innate immune system is an important mechanism of the host to defend against pathogens, especially for invertebrate, which lack adaptive immune systems
LysG1 was identified in the shrimp Rimicaris sp. from a hydrothermal vent in Desmos, Manus basin
It contains the conserved residues of the sugar binding site and catalytic site (E72 and D96) of g-type lysozyme
Summary
Accepted: 4 December 2021The innate immune system is an important mechanism of the host to defend against pathogens, especially for invertebrate, which lack adaptive immune systems. Lysozyme (muramidase, EC 3.2.1.17) is one of the key molecules of the innate immune system. It catalyzes the cleavage of the beta-1,4-glycosidic bond between the C-1 of N-acetylmuramic acid (MurNAc) and the C-4 of N-acetylglucosamine (GlcNAc) in peptidoglycan [1], an essential component of the bacterial cell wall. Lysozyme is widely employed by animals as a weapon against bacterial infection. Since, compared to Gram-negative bacteria, Gram-positive bacteria have a peptidoglycan cell wall that is much thicker and exposed to the extracellular milieu, lysozyme is generally more efficient at killing Grampositive bacteria. Some lysozymes are known to kill effectively Gram-negative bacteria [2,3,4,5]. Lysozyme has been reported to have functions other than muramidase, such as isopeptidase, chitinase, and non-enzyme antibacterial activities [5]
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