Reactive Cu2+-peptide intermediates revealed by kinetic studies gain relevance by matching time windows in copper metallomics

Abstract

The purpose of this essay is to propose that metallomic studies in the area of extracellular copper transport are incomplete without the explicit consideration of kinetics of Cu2+ion binding and exchange reactions. The kinetic data should be interpreted in the context of time constraints imposed by specific physiological processes. Examples from experimental studies of Cu2+ ion interactions with ATCUN/NTS (amino-terminal copper and nickel binding site/N-terminal site) motifs are used to demonstrate that duration and periodicity of such processes as bloodstream transport or neurotransmission promote the reaction intermediates to the role of physiological effectors. The unexpectedly long lifetimes of intermediate complexes lead to their accumulation and novel reactivities. The emerging ideas are discussed in the context of other research areas in metallomics.

Toward a Mechanism-Driven Integrated Framework to Link Human Exposure to Multiple Toxic Metal(loid) Species with Environmental Diseases

“…Taken together, these results demonstrate that in vitro studies can provide useful insight into dynamic aspects of the toxicological chemistry of individual metal(loid) species in blood plasma and that ternary interactions between a toxic metal(loid) species, a plasma protein and a SMW metabolite (e.g., Cys, hCys and/or others) that unfold in the presence of 100 mM Cl − play an important role in the selective delivery of their 'cargo' to toxicological target organs. These findings are reminiscent of previously observed interactions between Cu 2+ , HSA and L-histidine [95], the kinetic aspects of which are still not completely understood [96], and conceptually related studies which have demonstrated that the binding of Zn 2+ to HSA is modified by the fatty acid myristate, with health-relevant ramifications in the organs downstream [97]. While it cannot be entirely excluded that Hg 2+ -induced conformational changes of HSA [98] play an important role in its translocation to target organs, the obtained results suggest that probing ternary interactions between other neurotoxic metal(loid) species, such as Mn 2+ , As III and Pb 2+ with their known plasma proteins and distinct SMW metabolites in the presence of 100 mM NaCl may be a fruitful strategy to uncover the biomolecular mechanisms that deliver their cargo to uptake mechanisms at the blood-brain-barrier (BBB), which is a prerequisite for their subsequent uptake into the brain to cause neurotoxicity.…”

Glycyl-l-histidyl-l-lysine prevents copper- and zinc-induced protein aggregation and central nervous system cell death in vitro

“…Furthermore, GHK's ability to form ternary complexes with imidazole-containing peptides [including serum albumin's N-terminal site Asp-Ala-His (NTS)] and with GHK itself means that such ternary complexes are likely being formed under these experimental conditions that also may affect aggregation kinetics. 101 , 102 One study has demonstrated that a 5 mM concentration of GHK in conjunction with HSA and Cu 2+ leads to an increase in the prevalence of both binary Cu-(GHK) and ternary Cu-(GHK)N IM GHK complexes that together form more than 40% of the detected species, the rest being predominantly the Cu-(GHK)N IM HSA ternary complex, with a fraction being solely bound to HSA. 56 It would be possible that even a greater ratio of GHK-Cu binary and ternary complexes would be evident in this experiment as the ratio of GHK to BSA is even higher.…”

The Cu(Ii) Affinity Constant and Reactivity of Hepcidin-25, the Main Iron Regulator in Human Blood

“…This, according to our other studies, is dictated by very low k off values for the hepcidin's ATCUN motif. The k on has not been determined, but the formation of CuH25 4 N complex may take significantly <1 s, possibly sufficiently fast to maintain for a Cu(II) scavenger role [76,77]. Upon a rigorous in vitro test, the ability of pure α2M to bind Cu(II) ions was neglected [28].…”

“…The inertness of CuH25 in Cu(II) exchange reactions is another factor enhancing the likelihood of its contribution to Cu(II) blood homeostasis. Recent findings regarding kinetic properties of ATCUN/NTS complexes indicate the relevance of second-to-minute time windows in copper distribution from the intestine through blood to liver and other organs [76,77]. Under such conditions the CuH25 complex once formed may be sufficiently long-lived to exert its hypothetical copper-related functions before being cleared from the bloodstream or exchanging the Cu(II) ion.…”