Structure-function analysis of Friedreich's ataxia mutants reveals determinants of frataxin binding and activation of the Fe-S assembly complex

Biochemistry. 2011 Aug 23;50(33):7265-74. doi: 10.1021/bi200895k. Epub 2011 Aug 2.


Friedreich's 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-S 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-S 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-function studies reveal determinants for the binding and allosteric activation of the Fe-S assembly complex and provide insight into how FRDA missense mutations are functionally compromised.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation
  • Carbon-Sulfur Lyases / genetics
  • Carbon-Sulfur Lyases / metabolism
  • Crystallography, X-Ray
  • Enzyme Activation
  • Friedreich Ataxia / genetics
  • Friedreich Ataxia / metabolism*
  • Humans
  • Iron-Binding Proteins / chemistry*
  • Iron-Binding Proteins / genetics
  • Iron-Binding Proteins / metabolism*
  • Iron-Regulatory Proteins / metabolism
  • Iron-Sulfur Proteins / genetics
  • Iron-Sulfur Proteins / metabolism*
  • Kinetics
  • Models, Molecular
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism*
  • Mutation, Missense / genetics*
  • Protein Binding
  • Protein Conformation
  • Structure-Activity Relationship
  • Sulfides / metabolism*


  • ISCU protein, human
  • ISD11 protein, human
  • Iron-Binding Proteins
  • Iron-Regulatory Proteins
  • Iron-Sulfur Proteins
  • Mutant Proteins
  • Sulfides
  • frataxin
  • Carbon-Sulfur Lyases
  • NFS1 protein, human
  • cysteine desulfurase