Copper- and iron-dependent methane monooxygenases (MMOs) are essential enzymes in methanotrophic bacteria that oxidize methane to methanol, playing a critical role in regulating methane emissions, a potent greenhouse gas. The review discusses the structure, function, and mechanisms of two types of MMOs: the copper-dependent particulate methane monooxygenase (pMMO) and the iron-dependent soluble methane monooxygenase (sMMO). pMMO is a trimeric enzyme with three subunits (PmoB, PmoA, and PmoC), and its active site is believed to contain a mononuclear Cu(II) center. The sMMO, on the other hand, is a soluble enzyme with a dinuclear iron active site. Both enzymes are crucial for methane oxidation, and their regulation is influenced by copper availability, leading to a "copper switch" that determines which enzyme is active under different conditions. The review highlights recent advances in understanding the molecular mechanisms of these enzymes, including their structures, metal binding sites, and interactions with other proteins. It also discusses the challenges in developing efficient catalysts for direct methane conversion and the potential of bioengineered systems for climate change mitigation. The study emphasizes the importance of interdisciplinary approaches, including biochemistry, structural biology, and computational methods, in unraveling the complexities of MMOs and their applications in biotechnology.Copper- and iron-dependent methane monooxygenases (MMOs) are essential enzymes in methanotrophic bacteria that oxidize methane to methanol, playing a critical role in regulating methane emissions, a potent greenhouse gas. The review discusses the structure, function, and mechanisms of two types of MMOs: the copper-dependent particulate methane monooxygenase (pMMO) and the iron-dependent soluble methane monooxygenase (sMMO). pMMO is a trimeric enzyme with three subunits (PmoB, PmoA, and PmoC), and its active site is believed to contain a mononuclear Cu(II) center. The sMMO, on the other hand, is a soluble enzyme with a dinuclear iron active site. Both enzymes are crucial for methane oxidation, and their regulation is influenced by copper availability, leading to a "copper switch" that determines which enzyme is active under different conditions. The review highlights recent advances in understanding the molecular mechanisms of these enzymes, including their structures, metal binding sites, and interactions with other proteins. It also discusses the challenges in developing efficient catalysts for direct methane conversion and the potential of bioengineered systems for climate change mitigation. The study emphasizes the importance of interdisciplinary approaches, including biochemistry, structural biology, and computational methods, in unraveling the complexities of MMOs and their applications in biotechnology.