Tryptophan residue 32 in human Cu-Zn superoxide dismutase modulates prion-like propagation and strain selection
Anthony Crown1, Luke McAlary2,3, Eric Fagerli1
1Center for Translational Research in Neurodegenerative Disease, SantaFe HealthCare Alzheimer's Disease Research Center, Department of Neuroscience, McKnight Brain Institute, University of Florida, Gainesville, Florida, United States of America.
Abstract:
Mutations in Cu/Zn superoxide dismutase 1 (SOD1) associated with familial amyotrophic lateral sclerosis cause the protein to aggregate via a prion-like process in which soluble molecules are recruited to aggregates by conformational templating. These misfolded SOD1 proteins can propagate aggregation-inducing conformations across cellular membranes. Prior studies demonstrated that mutation of a Trp (W) residue at position 32 to Ser (S) suppresses the propagation of misfolded conformations between cells, whereas other studies have shown that mutation of Trp 32 to Phe (F), or Cys 111 to Ser, can act in cis to attenuate aggregation of mutant SOD1. By expressing mutant SOD1 fused with yellow fluorescent protein (YFP), we compared the relative ability of these mutations to modulate the formation of inclusions by ALS-mutant SOD1 (G93A and G85R). Only mutation of Trp 32 to Ser persistently reduced the formation of the amorphous inclusions that form in these cells, consistent with the idea that a Ser at position 32 inhibits templated propagation of aggregation prone conformations. To further test this idea, we produced aggregated fibrils of recombinant SOD1-W32S in vitro and injected them into the spinal cords of newborn mice expressing G85R-SOD1: YFP. The injected mice developed an earlier onset paralysis with a frequency similar to mice injected with WT SOD1 fibrils, generating a strain of misfolded SOD1 that produced highly fibrillar inclusion pathology. These findings suggest that the effect of Trp 32 in modulating the propagation of misfolded SOD1 conformations may be dependent upon the "strain" of the conformer that is propagating.
Insights
Mutations in copper/zinc superoxide dismutase 1 (SOD1) linked to familial amyotrophic lateral sclerosis can propagate misfolded conformations. A specific mutation, Trp 32 to Ser, effectively reduced protein aggregation and inclusion formation in cells.
Area of Science:
- Neuroscience
- Molecular Biology
- Protein Biochemistry
Background:
- Familial amyotrophic lateral sclerosis (ALS) is linked to mutations in copper/zinc superoxide dismutase 1 (SOD1).
- Misfolded SOD1 proteins aggregate and propagate via a prion-like mechanism, leading to cellular dysfunction.
- Specific mutations, such as Trp 32 to Ser, have been investigated for their potential to inhibit SOD1 misfolding and propagation.
Purpose of the Study:
- To compare the efficacy of different SOD1 mutations in modulating the formation of inclusions in ALS models.
- To investigate the role of Trp 32 residue in inhibiting the templated propagation of aggregation-prone SOD1 conformations.
- To determine if SOD1 conformation-modulating mutations are dependent on the propagating conformer strain.
Main Methods:
- Expression of mutant SOD1 fused with yellow fluorescent protein (YFP) in cellular models.
- Comparison of inclusion formation in cells expressing different SOD1 mutants (G93A, G85R).
- In vitro production of aggregated SOD1-W32S fibrils and subsequent injection into newborn mice expressing G85R-SOD1:YFP.
Main Results:
- Mutation of Trp 32 to Ser persistently reduced amorphous inclusion formation in cells.
- Injection of SOD1-W32S fibrils into mice expressing G85R-SOD1:YFP led to earlier onset paralysis and fibrillar inclusion pathology.
- The observed effects suggest that Trp 32's modulation of SOD1 propagation may be strain-dependent.
Conclusions:
- A Serine residue at position 32 of SOD1 effectively inhibits the templated propagation of aggregation-prone conformations.
- The impact of Trp 32 in modulating SOD1 misfolding propagation is influenced by the specific conformer strain involved.
- These findings offer insights into potential therapeutic strategies targeting SOD1 aggregation in ALS.
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