Q.35 Which of the following elements binds to protein and forms a critical DNA binding motif?
1. Manganese
2. Zinc
3. Cobalt
4. Copper
Zinc forms the critical zinc finger motif in proteins for DNA binding.
Zinc fingers are DNA-binding domains where Zn²⁺ coordinates with cysteine and histidine residues, stabilizing an α-helix that inserts into the DNA major groove for sequence-specific recognition in transcription factors like TFIIIA and Zif268.
Correct Answer
Option 2: Zinc.
Zinc tetrahedrally binds Cys₂His₂ in zinc finger motifs, enabling DNA interaction; over 700 human proteins use this for gene regulation.
Option Explanations
| Option | Element | Explanation |
|---|---|---|
| 1 | Manganese | Incorrect. Mn acts in enzymes (e.g., arginase, superoxide dismutase) as a cofactor but does not form structural DNA-binding motifs in proteins. |
| 2 | Zinc | Correct. Forms zinc finger (Cys₂His₂ or variants), a ubiquitous motif where Zn stabilizes finger-like structure for precise DNA major groove binding. |
| 3 | Cobalt | Incorrect. Co is rare in DNA-binding motifs; used in vitamin B12 or corrinoids, not protein-DNA structures. |
| 4 | Copper | Incorrect. Cu binds in enzymes (e.g., cytochrome c oxidase) or type 1 blue copper proteins but lacks a specific DNA-binding motif role. |
Exam Tip
Recall zinc fingers as classic eukaryotic DNA motifs; distinguish from leucine zippers (no metal) or helix-turn-helix.
