The pre-synaptic protein α-Synuclein (αS) is often linked to the pathology of Parkinson’s disease (PD), an age-related neurodegenerative disorder. Lewy bodies, the cytopathological hallmarks of PD, are found to be rich in aggregates of misfolded αS protein. Metal dyshomeostasis has also been linked to PD due to the accumulation of iron in the substantia nigra pars compacta, and diminished copper levels reported in this same region. Metal dyshomeostasis in the brain coupled with oxidative stress can enhance the aggregation of αS. Recently, it was confirmed that mammalian αS is universally acetylated at the N-terminus, a common post-translational modification in humans. The consequences of this modification have been understudied, and it is believed to impart a functional role under physiological conditions with respect to membrane-interactions and protein folding. In an attempt to elucidate the pathological mechanism behind PD with respect to the structural dynamics of the protein, our investigations were focused on physiologically prevalent, N-terminally acetylated αS (NAcαS) and its interaction with the most prevalent redox-active metal ions in the brain (iron and copper) under both aerobic and/or anaerobic conditions. The structural features associated with metal-bound NAcαS differed depending on the iron oxidation states, where under aerobic conditions Feᴵᴵ stabilized an oligomer-locked, anti-parallel right-twisted β-sheet conformation that could potentially impart toxicity to neurons. In contrast, Feᴵᴵᴵ promoted a fibrillar structure rich in parallel β-sheets. N-terminal capping also altered the Cuᴵᴵ coordination sphere and had a dramatic effect on protein aggregation. Parallel studies on NAcαS variants with different site mutations near the putative copper binding sites (ex: H50Q and F4W) indicated that preferential binding shifts upon changes in the side chain residues. In depth analysis of the electron structure of Cuᴵᴵ-bound NAcαS using electron paramagnetic resonance spectroscopy (EPR) revealed a coordination sphere of N3O1 that includes the H50 residue in the wild-type protein that shifts to an O4 coordination sphere at the C-terminus upon Cuᴵᴵ binding to the disease-relevant H50Q variant. Immunoblotting analyses revealed that copper-induced redox chemistry promoted O2-activation and the subsequent formation of dityrosine crosslinks, a post-translational modification identified as a biomarker of PD. EPR-detection of tyrosyl radical formation in the presence of Cuᴵ-bound NAcαS further supported this radical coupling mechanism. Intermolecular crosslinks within the fibrillar core of NAcαS as well as intramolecular crosslinks within the C-terminal region underpin the role of metal-dioxygen chemistry in PD-related pathology. The unique structural features resulting from iron vs copper coordination to NAcαS inspired studies directed at the synergistic effect of each individual metal species as revealed by photo-initiated crosslinking of NAcαS. C-terminal intramolecular tyrosine interactions were mainly impacted by the presence of both metals, which each have binding sites around the same region. These findings emphasize that protein dynamics, metal binding site conformational changes, as well as aggregation pathways can deviate drastically upon N-terminal acetylation of αS and that protein-metal interactions may play a vital role in PD etiology.

All cells maintain essential metal nutrients at optimal levels by metal homeostasis. P-type ATPases, a crucial superfamily of integral membrane proteins, are involved in the active transport of metal ions across biological membranes driven by the motive force of ATP- hydrolysis. The PIB-type ATPase subfamily, also called CPx-ATPases, fulfills a key role in heavy metal homoeostasis among the most widespread species from bacteria to human. In humans, the defect in copper transporters is the direct cause of severe neurological and hepatic disorders such as Wilson and Menkes diseases, therefore, understanding the molecular function of these pumps is of paramount importance in human health. Cu+-ATPases have two transmembrane metal binding sites (TM-MBS) and three cytosolic domains, namely the actuator (A-domain) and phosphorylation and nucleotide-binding domain (PN), and regulatory N-terminal heavy metal binding domain (HMBD). Here, we have studied the Legionella pneumophila CopA (LpCopA) and its isolated cytosolic domains to improve our understanding of the functional interaction of the protein domains during metal transport relate this to the known structure of this ATPase. To elucidate how cytosolic ligands (Cu+ and nucleotide) stimulate the interactions among the cytosolic domains and may transmit conformational changes to the TM-MBS, the interactions among recombinant isolated cytosolic domains were first examined biochemically by co-purification and spectroscopically by circular dichroism, time-resolved fluorescence and site-directed fluorescent labeling assays. The Cu+-dependent interaction between the A-domain and HMBD has been postulated as a mechanism for activating the ATPase cycle. This question was addressed here by studying copper-dependent interactions between the isolated expressed domains. Spectroscopic evidence is provided that an HMBD-A complex is formed in the presence of Cu+ which binds with 100-200 nM affinity to the recombinant HMBD. In contrast, the A-domain interacts with the PN domain in a nucleotide-dependent fashion. This molecular recognition is required for the dephosphorylation step in the catalytic cycle. The interaction was investigated in more detail by the use of a decameric peptide derived from the PN-binding interface of the A-domain and carrying the conserved TGE-motif involved in dephosphorylation. Its binding to the isolated PN domain in a weakly nucleotide-dependent manner, is demonstrated here by stopped-flow fluorescence spectroscopy. Several ATPase assays were modified to assess the functionality of the PN-domain and full length LpCopA. The peptide was found to reduce the catalytic turnover of full length LpCopA. This agrees with the expected slowing down of the reformation of the PN-A-domain interaction since the peptide occupies their binding interface. Thus, the synthetic peptide provides a means to study specifically the influence of PN-A-domain interactions on the structure and function of LpCopA. This was done by time-correlated single photon counting (TCSPC) method. The time-dependent Stokes shift of the environmentally sensitive fluorophore BADAN which was covalently attached to the conserved CPC-motif in the TM-MBS was measured. The data indicate that the interior of the ATPase is hydrated and the mobility of the intra-protein water varies from high to low at C382 at the “luminal side” and C384 at the “cytosolic side” of the TM-MBS, respectively. This finding is consistent with the recent MD simulation of LpCopA, bringing the first experimental evidence on a luminal-open conformation of E2~P state. The A-domain-derived decapeptide, although binding to the cytosolic head piece, induces structural changes also at the TM-MBS. The peptide-stabilized state (with a disrupted PN-A interface) renders the C384 environment more hydrophobic as evidenced by TCSPC. Taken together, the data from cytosolic domain interactions, ATPase assays and of time-dependent Stoke shift analyses of BADAN-labeled LpCopA reveal the presence of hydrated intramembraneous sites whose degree of hydration is regulated by the rearrangement of cytosolic domains, particularly during the association and dissociation of the PN-A domains. Copper affects this arrangement by inducing the linkage of the A-domain to the HMBD. The latter appears to play not only an autoinhibitory but also a chaperone-like role in transferring Cu+ to the TM-MBS during catalytic turnover.