35. β-α-β motif is composed of two beta strands joined by an alpha helix through connecting loops. This motif is known for
(1) ligand binding
(2) stereological hindrance in binding of ligand
(3) catalytic center
(4) transmembrane domain

The β-α-β Motif: Structure, Function, and Role in Ligand Binding

Protein motifs are fundamental building blocks that contribute to protein stability and function. The β-α-β motif is a widely occurring secondary structure element that plays a crucial role in protein-ligand interactions. Understanding this motif is essential for CSIR NET Life Science aspirants.

Correct Answer:

The correct option is (1) Ligand binding.

Explanation:

Structure of the β-α-β Motif

• The β-α-β motif consists of two parallel β-strands connected by an α-helix through loop regions.
• It forms a key structural component of α/β domains, frequently found in Rossmann folds and TIM barrels.
• The hydrophilic α-helix is positioned between two hydrophobic β-strands, stabilizing the motif.

(1) Ligand Binding ✅

• The β-α-β motif is a major ligand-binding site in many enzymes and proteins.
• Example: Rossmann fold, which binds nucleotide cofactors (e.g., ATP, NADH, FAD).
• The helix-loop region provides a pocket that interacts with substrates or cofactors.
• Found in enzymes like kinases, dehydrogenases, and ATP-binding proteins.

(2) Stereological Hindrance in Binding of Ligand ❌

• Instead of hindering ligand binding, the β-α-β motif enhances it by forming a stable interaction pocket.

(3) Catalytic Center ❌

• While the β-α-β motif contributes to enzyme structure, the catalytic center is usually composed of specific active site residues rather than just secondary structural motifs.

(4) Transmembrane Domain ❌

• Transmembrane domains are typically α-helical or β-barrel structures.
• The β-α-β motif is primarily soluble and found in globular proteins, not transmembrane proteins.

Nearby Topics for Better Understanding

1. Functional Importance of β-α-β Motifs

• Found in nucleotide-binding domains (e.g., ATPase, NADH-binding enzymes).
• Contributes to enzyme-substrate specificity.
• Present in signal transduction proteins.

2. Comparison of Protein Motifs

3. Importance of Ligand Binding in Enzymes

• Determines substrate specificity.
• Helps in cofactor association (e.g., Mg²⁺ in ATP-binding proteins).
• Regulates protein-protein interactions.

4. Clinical Significance of Ligand-Binding Proteins

• Kinases use β-α-β motifs for ATP binding (targeted in cancer therapy).
• Dehydrogenases bind NADH/NAD+ (important in metabolism).
• Antibody-antigen recognition relies on structured binding motifs.

Conclusion

The β-α-β motif is a crucial ligand-binding element found in enzymes and nucleotide-binding proteins. It stabilizes interactions with cofactors, aiding in enzymatic function. Mastering this concept is vital for CSIR NET Life Science aspirants studying protein structure and function.