Proton-dependent multidrug efflux systems are crucial for bacterial and eukaryotic cells to resist toxic compounds and maintain homeostasis. These systems are often energy-dependent, utilizing either ATP hydrolysis or the proton motive force (PMF). The major facilitator superfamily (MFS), resistance/nodulation/cell division (RND), and small multidrug resistance (SMR) families are key in this process. The MFS includes proteins like QacA and EmrB, which use PMF for drug efflux, while the RND family includes MexB, and the SMR family includes Smr. These systems are widespread across organisms, from bacteria to humans, and are involved in various physiological roles, including drug resistance and nutrient uptake. The MFS is divided into several families, with the 14-TMS and 12-TMS families being the most significant for multidrug efflux. The 14-TMS family includes proteins like QacA and EmrB, which are involved in effluxing a wide range of structurally diverse compounds. The 12-TMS family includes proteins like Bmr, Blt, and NorA, which also contribute to multidrug resistance. Additionally, VMAT1 and VMAT2, which are part of the 12-TMS family, are involved in neurotransmitter transport and have been shown to mediate drug resistance by accumulating toxic compounds in intracellular vesicles. Other PMF-dependent multidrug efflux systems include proteins like LmrP, Bcr, and EmrD, which are involved in effluxing various substrates. The study highlights the importance of these systems in clinical settings, as they can confer resistance to a broad spectrum of chemotherapeutic drugs. The molecular mechanisms underlying these systems involve the use of PMF, with some proteins requiring auxiliary proteins for efficient drug efflux. The structural and functional analysis of these proteins provides insights into their roles in drug resistance and the broader physiological functions of PMF-dependent transport systems.Proton-dependent multidrug efflux systems are crucial for bacterial and eukaryotic cells to resist toxic compounds and maintain homeostasis. These systems are often energy-dependent, utilizing either ATP hydrolysis or the proton motive force (PMF). The major facilitator superfamily (MFS), resistance/nodulation/cell division (RND), and small multidrug resistance (SMR) families are key in this process. The MFS includes proteins like QacA and EmrB, which use PMF for drug efflux, while the RND family includes MexB, and the SMR family includes Smr. These systems are widespread across organisms, from bacteria to humans, and are involved in various physiological roles, including drug resistance and nutrient uptake. The MFS is divided into several families, with the 14-TMS and 12-TMS families being the most significant for multidrug efflux. The 14-TMS family includes proteins like QacA and EmrB, which are involved in effluxing a wide range of structurally diverse compounds. The 12-TMS family includes proteins like Bmr, Blt, and NorA, which also contribute to multidrug resistance. Additionally, VMAT1 and VMAT2, which are part of the 12-TMS family, are involved in neurotransmitter transport and have been shown to mediate drug resistance by accumulating toxic compounds in intracellular vesicles. Other PMF-dependent multidrug efflux systems include proteins like LmrP, Bcr, and EmrD, which are involved in effluxing various substrates. The study highlights the importance of these systems in clinical settings, as they can confer resistance to a broad spectrum of chemotherapeutic drugs. The molecular mechanisms underlying these systems involve the use of PMF, with some proteins requiring auxiliary proteins for efficient drug efflux. The structural and functional analysis of these proteins provides insights into their roles in drug resistance and the broader physiological functions of PMF-dependent transport systems.