The interaction of the small (140 amino acid) protein, alpha-synuclein (alpha S), with Cu2+ has been proposed to play a role in Parkinson's disease (PD). While some insight from truncated model complexes has been gained, the nature of the corresponding Cu2+ binding modes in the full length protein remains comparatively less well characterized. This work examined the Cu2+ binding of recombinant human alpha S using Electron Paramagnetic Resonance (EPR) spectroscopy. Wild type (wt) alpha S was shown to bind stoichiometric Cu2+ via two N-terminal binding modes at physiological pH. An H50N mutation isolated one binding mode, whose g(parallel to), A(parallel to), and metal-ligand hyperfine parameters correlated well with a {NH2, N-, beta-COO-, H2O) mode previously identified in truncated model fragments. Electron spin-echo envelope modulation (ESEEM) studies of wt aS confirmed the second binding mode at pH 7.4 involved coordination of His50 and its g(parallel to), and A(parallel to) parameters correlated with either {NH2, N-, beta-COO-, N-lm} or {N-lm, 2N(-)} coordination observed in alpha S fragments. At pH 5.0, His50-anchored Cu2+ binding was greatly diminished, while {NH2, N-, beta-COO-, H2O} binding persisted in conjunction with another two binding modes. Metal-ligand hyperfine interactions from one of these indicated a 1N3O coordination sphere, which was ascribed to a (NH2, CO) binding mode. The other was characterized by a spectrum similar to that previously observed for diethylpyrocarbonate-treated alpha S and was attributed to C-terminal binding centered on Asp121. In total, four Cu2+ binding modes were identified within pH 5.0-7.4, providing a more comprehensive picture of the Cu2+ binding properties of recombinant alpha S.