CHAPERONE TARGET INTERACTIONS

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Copper is an essential element in eukaryotic organisms. Due to facile redox chemistry at moderate potentials, it functions at the active sites of many critical enzymes involved in a wide variety of processes, including neurotransmitter and neuropeptide hormone biosynthesis, biogenic amine metabolism and connective tissue formation, pigmentation, respiration, and antioxidant defense. New findings have linked certain cancers to copper mediated enzyme activity, for example the observation that the expression of the cuproenzyme PAM in endocrine tumors mediates tumor growth. Another intriguing link of importance to cancer therapy, is the recruitment of the CTR1 high affinity copper transporter in the uptake of cis-platin into cells by a presently unknown mechanism. Because copper is both essential and potentially toxic, cells have evolved complex molecular machinery to maintain levels within a narrow range of concentration, and failure to achieve liomeostasis results in diseases related to either Cu deficiency or excess which include those involving genetic mutations in the copper transporting ATPases, ATP7A (Menkes disease) and ATP7B (Wilson disease). Important consequences of aberrant copper homeostasis have also been implicated in neurodegenerative disorders, and in the pathology of amyloid plaque formation in Alzheimers. Therefore, the study of copper uptake, transport and trafficking is of great importance to human health. In eukaryotes, copper is imported by the membrane associated high affinity transporter CTR1, and thence distributed to target proteins via metallochaperone shuttles. An important tenet of copper homeostasis is the hypothesis that CTR1 hands off copper to the chaperones which in turn transport the metal to its sites of action. However, the interaction of CTR1 with chaperones has not yet been experimentally verified. Project 2 of the PPG will therefore leverage recent advances in the structural biology of hCTRl to investigate (i) the mode of copper binding to CTR1, (ii) the interaction of CTR1 with the chaperone hCCS, and (iii) the mechanisms by which chaperones and ATPases interact with and transfer copper to their target cuproenzymes. The technique of selenium-labeling coupled to X-ray absorption spectroscopy (developed in the last grant period) will be used extensively in these studies.