Nuclear Receptor DNA Interactions: Zinc Fingers

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Nuclear Receptor - DNA InteractionsZinc Fingers

• Kylie Graham

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Zinc Fingers
Classic Zn Finger, C2H2
C4 Zinc Fingers
C6 Zinc Fingers
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Nuclear Receptors are ligand activated
Transcription Factors

• Receptors bind HRE at DNA binding domain (BD)
• BD is the most conserved structural element

DNA BD
Adapted From Biochemistry of Signal Transduction
and Regulation. Krauss. Fig 4.8
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DNA Binding Domain

• BD structure mediates
• specific recognition of HRE
• Dimerization of receptor on HRE
• Core of 70-80 amino acids
• 2 Cys4 Zinc Finger motifs
• Position recognition helix in major groove
• Contacts formed with bases of DNA through
  H-bonding

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Cys4 Zinc Finger Motifs

• 1st discovered in steroid
• hormone receptors
• DNA Binding Domain
• consensus sequence
• Cys-X2-Cys-X13-Cys-X2-Cys-X14-15-Cys-X5-Cys-X9-Cys
  -X2-Cys
• 4 critical Cys bind 1 Zn2
• Two fingers one
• structural unit

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Cys4 Zinc Finger Motifs

• 3 ? helices are packed together with aid of
  coordinated Zn2 ions
• 1st finger of motif has P-box for DNA specificity
  sequence discrimination
• Inserted in major groove
• 2nd finger folded into helices 2 3 for
  DNA-dependent dimerization
• Helices 1 3 are perpendicular to each other

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How was this discovered?

• Domain Swapping Experiments
• Construct chimeric DNA binding domains
• Found 1st finger important for DNA binding
• Mutational Analysis
• Found 3 key residues in 2nd zinc finger involved
  in dimerization

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Cys4 Zinc Finger Motifs
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Cys4 Zinc Finger Motifs
http//www.neurosci.pharm.utoledo.edu/MBC3320/ster
oids.htm
http//www.cas.psu.edu/docs/CASDEPT/VET/classes/vs
c597b/CMMT20597b20lecture204.html
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Specificity

• Remember the binding domain has a consenses
  sequence.
• Class I receptors (GR, PR, MR, AR) all recognize
  inverted repeats of 5-TGTTCT-3 with a 3 base
  spacer
• So how are the specific steroid responses
  mediated???
• Move on to look at dimerization other
  coactivator proteins!