Methane gas is the second most potent greenhouse gas after carbon dioxide and contributes significantly to the Earth’s rising temperature. Methane-oxidizing bacteria (MOB), known as methanotrophs, use methane as their only carbon and energy source, acting as a methane sink. The first step in the methanotroph metabolic pathway is the conversion of methane to methanol by the particulate methane monooxygenase enzyme (pMMO), which requires copper. However, a complete understanding of pMMO has been hindered by the low enzymatic activity observed during its isolation and purification. This reduced activity may result from the absence of partner proteins that are lost during purification. Such proteins may be crucial for the function of pMMO, assisting in metal acquisition, maintaining a specific redox state, protecting against oxygen radicals, and delivering electrons or protons to the active site. One uncharacterized protein that may fulfill these roles is the soluble small metal-binding protein (SmbP), which is abundant in MOB. Previous studies on SmbP from ammonia-oxidizing bacteria (AOB) suggested a role in the cellular management of copper,1 though this hypothesis lacks experimental support. We have expressed SmbP fromMethylococcus capsulatus (Bath) in E. coli. ICP-MS analysis indicates that SmbP selectively binds one equivalent of copper, also evidenced by the presence of an optical d-d* transition band at ~630 nm. The EPR spectrum of Cu-SmbP is consistent with a type 2 Cu site, and 2H and 15N ENDOR provide additional insight into the primary coordination sphere of Cu bound to SmbP. Progress toward establishing the role of SmbP in M. capsulatus (Bath) physiology will also be reported.