Investigation of mutated CuZn Superoxide Dismutase

1
Investigation of mutated Cu/Zn Superoxide
Dismutase

• Sam Schuberg
• Beckman Laboratory
• Howard Hughes Medical Institute Summer 2007

2
Amyotrophic Lateral Sclerosis

• Neurodegenerative disease caused by the
  destruction of the motor neurons along the spinal
  cord
• Gradual loss of voluntary muscular function
• Not only difficulty in moving, but also in
  speaking and swallowing
• Eventually affects respiratory system

3
Types of ALS

• Two types of ALS
• Sporadic and Familial
• 98 of patients have sporadic ALS
• 2 have genetically inherited the disease
• Nature 1993
• Common link in a mutation in chromosome 21
• The gene with the mutations is for SOD1
• Currently over 100 mutations identified

Beckman et al. Superoxide dismutase and the death
of motor nuerons in ALS. Trends Nueroscience,
2001.
4
Wild Type Superoxide Dismutase

• Scavenges superoxide produced by normal
  metabolism
• The dimer interface is stabilized by a disulfide
  bond
• A cytosolic disulfides
• Active site contains two metal ions
• Rate 2 x 109 M-1s-1

5
Mutated SOD

• It is widely accepted that these mutations not
  only deactivate SOD1s scavenging feature, but
  cause it to gain a toxic function
• Debate is on what this toxic function is
• One theory is aggregation

6
The hypothesis of Zn deficient SOD

• Mutations destabilize the enzyme and cause it to
  lose its affinity for Zn
• Alters coordination of the neighboring Cu through
  a shared histidine ligand
• The exposed Cu is readily reduced by antioxidents
  
• Reduced Cu donates an electron to oxygen to
  produce superoxide
• O2.- react with NO to form peroxynitrite
• Peroxynitrite modifies important biological
  molecules leading to apoptosis

Beckman et al. Superoxide dismutase and the death
of motor nuerons in ALS. Trends Nueroscience,
2001.
7

• Dr. Wang and his research group created
  SOD-mutated mice deficient in four histidines
• These coordinate and hold Cu in its active site
• Their quad mice still get ALS like symptoms
• Their in vitro data was interpreted as consistent
  with aggregation
• Their data suggests that CuII is not important
  in disease pathology

Cu
Wang et al. Journal of Neuroscience.
Copper-binding-site-null SOD1 causes ALS in
transgenic mice aggregates of non-native SOD1
delineate a common feature. 2003.
8
My project

• To further investigate the aggregation of mutant
  superoxide dismutases in spinal cord punches from
  transgenic mice.

9
Spinal cord punches
10
Do the Quad and G93A mutants aggregate in animals?

• Western Blot Analysis
• Location of SOD1
• Supernatant versus pellet
• Mice
• Mutated SOD1
• Quad and G93A
• Punches from the spinal cords
• ventral and dorsal side are taken

11
Mutated SOD is primarily located in the
supernatant
Homozygous Quad 210 days
Heterozygous Quad 210 days
Heterozygous Quad 190 days
G93A 80 days
63.12 ng SOD std
15.78 ng SOD std
15.78 ng SOD std
31.56 ng SOD std
63.12 ng SOD std
31.56 ng SOD std
Pellet
Pellet
Pellet
Pellet
Supernatant
Supernatant
Supernatant
Supernatant
Pellet
Pellet
Pellet
Pellet
Supernatant
Supernatant
Supernatant
Supernatant
ventral
ventral
dorsal
dorsal
ventral
ventral
dorsal
dorsal
12
Conclusions

• My results are not consistent with aggregation
• Previous results could be artifacts of sonication
  and grinding of the spinal cord

13
Acknowledgments

• Howard Hughes Medical Institute
• Dr. Joseph Beckman, Nathan Lopez and the Beckman
  Lab
• Dr. Kevin Ahern