Structure鈥揊unction Analysis of Friedreich鈥檚 Ataxia Mutants Reveals Determinants of Frataxin Binding and Activation of the Fe鈥揝 Assembly Complex

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• 作者：Jennifer Bridwell-Rabb ; Andrew M. Winn ; David P. Barondeau
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：August 23, 2011
• 年：2011
• 卷：50
• 期：33
• 页码：7265-7274
• 全文大小：691K
• 年卷期：v.50,no.33(August 23, 2011)
• ISSN：1520-4995

文摘

Friedreich鈥檚 ataxia (FRDA) is a progressive neurodegenerative disease associated with the loss of function of the protein frataxin (FXN) that results from low FXN levels due to a GAA triplet repeat expansion or, occasionally, from missense mutations in the FXN gene. Here biochemical and structural properties of FXN variants, including three FRDA missense mutations (N146K, Q148R, and R165C) and three related mutants (N146A, Q148G, and Q153A), were determined in an effort to understand the structural basis for the loss of function. In vitro assays revealed that although the three FRDA missense mutations exhibited similar losses of cysteine desulfurase and Fe鈥揝 cluster assembly activities, the causes for these activation defects were distinct. The R165C variant exhibited a k_cat/K_M higher than that of native FXN but weak binding to the NFS1, ISD11, and ISCU2 (SDU) complex, whereas the Q148R variant exhibited the lowest k_cat/K_M of the six tested FXN variants and only a modest binding deficiency. The order of the FXN binding affinities for the SDU Fe鈥揝 assembly complex was as follows: FXN > Q148R > N146A > Q148G > N146K > Q153A > R165C. Four different classes of FXN variants were identified on the basis of their biochemical properties. Together, these structure鈥揻unction studies reveal determinants for the binding and allosteric activation of the Fe鈥揝 assembly complex and provide insight into how FRDA missense mutations are functionally compromised.