Question

Why is it that membrane spanning protein segments are almost always alpha helices or Beta barrels but never disordered chains?

Can someone please help me understand this, it was a question in my class that was never fully explained. Thank you.

Answer 1

Membrane proteins are present in biological membrane and participate in various biological functions like signal transduction pathways.

Transmembrane proteins span across the membrane once or several times in weaving pattern.

Alpha helical transmembrane proteins composed of hydrophobic amino acid residues and little hydrophillic residues.

Beta barells cross cellular membrane and acts as a pore through which molecules can diffuse.

In both alpha helix and beta barell,the polar H-bonding groups in the peptide bond make internal hydrogen bonds with other peptide bonds.In a disordered chain the peptide polar groups are not bonded to each other or to a lipid .As a result ,a disordered peptide chain in a membrane is energetically very un favorable.