Tetracycline-inactivating monooxygenase Tet(X) (Tet(X))

Tetracycline-inactivating monooxygenase Tet(X) is a flavin-dependent enzyme that provides bacteria with a potent mechanism of resistance against the tetracycline class of antibiotics. Unlike common resistance mechanisms such as efflux pumps or ribosomal protection, Tet(X) chemically modifies and degrades the antibiotic molecule itself. It specifically catalyzes the hydroxylation of the C11a position of the tetracycline scaffold, leading to the spontaneous decomposition of the drug (Yang et al., 2014, J. Biol. Chem.). This enzyme is of significant clinical concern because it can inactivate even the latest generation of tetracyclines, such as tigecycline and eravacycline, which are often used as last-resort treatments (He et al., 2019, Nature Microbiology). The genes encoding Tet(X) variants, particularly Tet(X4), are frequently located on mobile genetic elements, facilitating their rapid spread among diverse bacterial pathogens (Sun et al., 2019, Nature Microbiology). Consequently, Tet(X) has become a primary target for the development of adjuvant therapies designed to inhibit the enzyme and restore antibiotic sensitivity. This enzymatic degradation represents a major hurdle in treating multi-drug resistant infections, particularly those caused by Gram-negative bacteria. Understanding the structural and functional nuances of Tet(X) is essential for the design of next-generation tetracyclines that are resistant to enzymatic cleavage.

Other names

TetXFlavin-dependent tetracycline monooxygenaseTetracycline-destructive enzymeTetracycline 11a-hydroxylase

Tet(X) catalyzes the NADPH-dependent and oxygen-dependent hydroxylation of tetracyclines at the C11a position, resulting in a fragile intermediate that undergoes spontaneous non-enzymatic degradation, thereby inactivating the antibiotic (Yang et al., 2014, J. Biol. Chem.).