Banci L, Bertini I, Boca M, Calderone V, Cantini F, Girotto S, Vieru M. Structural and dynamic aspects related to oligomerization of apo SOD1 and its mutants. Proc Natl Acad Sci U S A. 2009 Apr 28;106(17):6980-5. PubMed.

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  1. This study characterizes the dynamic behavior of SOD1 in detail. First, it essentially reproduces previous studies including the ones from the authors' group, as it has been well known that overall structures are similar between wild-type and mutant SOD1 proteins. In addition, significant differences in the dynamic behavior have been observed between Apo and holo forms of SOD1. When the metal ions are removed from the protein, structural disorder increases particularly in the loop regions.

    We think that one of the interesting findings in this paper is the increased solvent accessibility of Cys-6 upon metal removal. Cys-6 is one of the four Cys residues (Cys-6, 57, 111, 146) in SOD1 and is buried toward the protein interior in the holo form of SOD1. In an enzymatically active form of SOD1, an intra-molecular disulfide forms between Cys-57 and 146, while Cys-6 and 111 remain reduced. In contrast, pathological inclusions purified from several ALS-model mice contain SOD1 multimers that are cross-linked via non-physiological disulfide bonds (Furukawa et al., 2006).

    It is, however, still controversial which Cys residues are involved in the formation of cross-linked SOD1 multimers under pathological conditions. While we have previously reported that the disulfide formation is not absolutely required for triggering SOD1 aggregation (Furukawa et al., 2008), an important role of Cys-6 and 111 in the formation of disulfide cross-links has been also suggested in the cultured cell model (Niwa et al., 2007). In addition, ALS-causing mutations at position 6 have been reported (i.e., C6G and C6F), implying that the other Cys residues are involved in the formation of disulfide-linked multimers even when Cys-6 is unavailable for disulfide formation. Nonetheless, the increased flexibility and solvent accessibility of Cys-6 upon metal removal will be an important clue to explain a molecular mechanism of the pathological SOD1 oligomer formation.

    References:

    Furukawa Y, Fu R, Deng HX, Siddique T, O'Halloran TV. Disulfide cross-linked protein represents a significant fraction of ALS-associated Cu, Zn-superoxide dismutase aggregates in spinal cords of model mice. Proc Natl Acad Sci U S A. 2006 May 2;103(18):7148-53. PubMed.

    Furukawa Y, Kaneko K, Yamanaka K, O'Halloran TV, Nukina N. Complete loss of post-translational modifications triggers fibrillar aggregation of SOD1 in the familial form of amyotrophic lateral sclerosis. J Biol Chem. 2008 Aug 29;283(35):24167-76. PubMed.

    Niwa J, Yamada S, Ishigaki S, Sone J, Takahashi M, Katsuno M, Tanaka F, Doyu M, Sobue G. Disulfide bond mediates aggregation, toxicity, and ubiquitylation of familial amyotrophic lateral sclerosis-linked mutant SOD1. J Biol Chem. 2007 Sep 21;282(38):28087-95. PubMed.

    View all comments by Yoshiaki Furukawa

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