A study recently published in the journal Nucleic Acids Research by Dr. Gloria del Solar's group at the Margarita Salas Center for Biological Research (CSIC) shows how is initiated the replication of a family of plasmids - extrachromosomal DNA molecules with the ability to replicate autonomously in bacteria - that can contain antibiotic resistance genes and be transferred horizontally from one bacterium to another.
DNA replication is an essential process for all living organisms, as it ensures the inheritance of genetic material to daughter cells from cell division. One of the replication initiation mechanisms is known as the "rolling circle", which is used by certain viruses, bacteriophages, and plasmids. This is the case of plasmid pMV158, isolated from a pathogenic strain of Streptococcus agalactiae and carrying a tetracycline resistance gene, whose replication initiation is catalyzed by the RepB protein.
The study, led by Prof. Miquel Coll (IRB, IBMB-CSIC) and Dr. Gloria del Solar (CIB-CSIC), and whose first authors are Dr. Cristina Machón (IRB) and Dr. José Ángel Ruiz-Masó (CIB-CSIC), reveals the molecular mechanism by which the origin of replication of plasmid pMV158, which can be mobilized to a large number of bacterial genera and species, is recognized explicitly by the replication initiator protein (RepB), encoded by this plasmid.
Machón et al. show, for the first time, the atomic structure of the initiator protein linked to the replication origin of this promiscuous plasmid. Using molecular biology, biochemistry, and X-ray crystallography techniques, the researchers have characterized a new hexameric structure of the RepB protein, as well as how it binds to DNA. The structure suggests that this protein has enormous flexibility, allowing it to interact with different elements of the plasmid's origin of replication and make a specific cut in one of the DNA strands, thus generating a substrate for DNA synthesis.
The work sheds light on the DNA replication of genetic elements involved in the spread of antibiotic resistance. Although this is basic research work, knowledge of the mechanism by which the replication initiator protein recognizes the origin of a plasmid that can confer antibiotic resistance to a wide variety of bacteria could be useful in addressing the growing and serious global health problem posed by the spread of bacterial resistance to antimicrobials. The design of new compounds -or the reuse of some previously used for other purposes- capable of blocking the interaction between the initiator protein and the DNA of the plasmid origin, so as to selectively prevent the propagation of the plasmid and, therefore, the dissemination of the antibiotic resistance determined by it, without affecting the viability of the beneficial bacteria that make up the human microbiota, could be contemplated.
Reference: Structures of pMV158 replication initiator RepB with and without DNA reveal a flexible dual-function protein. Cristina Machón, José Ángel Ruiz-Masó, Juliana Amodio, D Roeland Boer, Lorena Bordanaba-Ruiseco, Katarzyna Bury, Igor Konieczny, Gloria del Solar, Miquel Coll (2023) Nucleic Acids Research, 51:3, 1458–1472. https://doi.org/10.1093/nar/gkac1271