Need help on a question about Proteins

Describe three structural motifs used by proteins to span the lipid bilayer. What do all of these motifs have in common that suit them to this purpose?

I know that there are α-helices which consist only of hydrophobic residues and β-sheets that fold into β-barrels with aromatic resides on the outside. I also know that there would be helix-loop-helix motifs and β-hairpin loops. What else am I missing from my answer? I know that the secondary structures are able to span the membrane by forming hydrophobic interactions with the fatty acid tails and the motifs that I mentioned would allow the α and β-units to make abrupt turns and are located facing the solution. What else should I add?

Reply 1

macpatgh-Sheldon

20

Hi,
You could mention the Greek key motif: a beta hairpin folded over to form a 4-strand antiparallel beta sheet, although I can't explain how it would promote a protein spanning the cell membrane (perhaps this motif, the beta-alpha-beta motif and the alpha-alpha motif sort of "hide" the hydrophilic R groups of certain amino acids between the folded chains to bypass the lack of affinity for the hydrophobic tails of the lipid bilayer.

You could also refer to and describe the terms "supersecondary structure" and "domains" - would the latter be the explanation for the common features of the motifs (2nd part of Q), OR it might be the fact that folding conceals the hydrophilic parts??

M

Reply 2

Archurus23

OP

21

Original post by macpatgh-Sheldon

Hi,
You could mention the Greek key motif: a beta hairpin folded over to form a 4-strand antiparallel beta sheet, although I can't explain how it would promote a protein spanning the cell membrane (perhaps this motif, the beta-alpha-beta motif and the alpha-alpha motif sort of "hide" the hydrophilic R groups of certain amino acids between the folded chains to bypass the lack of affinity for the hydrophobic tails of the lipid bilayer.

You could also refer to and describe the terms "supersecondary structure" and "domains" - would the latter be the explanation for the common features of the motifs (2nd part of Q), OR it might be the fact that folding conceals the hydrophilic parts??

M

Thank you very much. Oh hello again

(edited 5 years ago)

Reply 3

macpatgh-Sheldon

20

Haiya,

Hope you are keeping well! Keep working hard as you are already doing - everything will fall into place in due course!

M

Reply 4

Archurus23

OP

21

Thank you. I'm doing my best at least. Thank you for getting back to me. How are you? May I please ask you another question?

Original post by macpatgh-Sheldon

Haiya,

Hope you are keeping well! Keep working hard as you are already doing - everything will fall into place in due course!

M

Reply 5

macpatgh-Sheldon

20

Ok go ahead, but I am only human - even Sheldon has a limit of 10E13 synapses in the brain, so may not know the answer! Yeah thanks I am well with the hockey match last Sat + badminton 4 times a week + cycling + some good grub - I am OK!

Reply 6

Archurus23

OP

21

The relationship between the amino-acid sequence of a protein and its three-dimensional structure was once thought to be straightforward: unique sequence determines unique 3d structure. Yet despite the enormous diversity of protein sequences, the number of distinct folds adopted by proteins in nature appears to be limited. How can we rationalise these two apparently contradictory ideas?

The only thing I can think of at the moment is that the proteins may have a similar amino acid composition or an evolutionary relationship. I know there's more to though but I can't really think of anything.

Original post by macpatgh-Sheldon

Ok go ahead, but I am only human - even Sheldon has a limit of 10E13 synapses in the brain, so may not know the answer! Yeah thanks I am well with the hockey match last Sat + badminton 4 times a week + cycling + some good grub - I am OK!