Extracting peripheral membrane proteins?

[Fanghur]

I'm confused about something; my lecture notes say (or at least that's how they sound) that if a detergent or phospholipase can remove a protein from the cell membrane, then that protein must be integral. Now, I can understand why detergents and phospholipases can extract transmembrane and lipid-anchored proteins (i.e. integral membrane proteins), but wouldn't they also disrupt the hydrogen bonds and salt bridges of, and thus extract peripheral membrane proteins as well? At least detergents, I'm not sure about phospholipases.

 

I find it strange that detergents wouldn't also remove peripheral proteins from the membrane in addition to integral proteins, since logically if you disrupt the membrane, you'll also disrupt what is on the surface of the membrane.

 

Can someone clarify this for me?

[D.Smalley]

I'm confused about something; my lecture notes say (or at least that's how they sound) that if a detergent or phospholipase can remove a protein from the cell membrane, then that protein must be integral. Now, I can understand why detergents and phospholipases can extract transmembrane and lipid-anchored proteins (i.e. integral membrane proteins), but wouldn't they also disrupt the hydrogen bonds and salt bridges of, and thus extract peripheral membrane proteins as well? At least detergents, I'm not sure about phospholipases.

 

I find it strange that detergents wouldn't also remove peripheral proteins from the membrane in addition to integral proteins, since logically if you disrupt the membrane, you'll also disrupt what is on the surface of the membrane.

 

Can someone clarify this for me?

 

Well, this is what I think: The main thing to remember is that integral membrane proteins are in the membrane because they are hydrophobic, peripheral proteins are not in the membrane because they are hydrophilic. Hopefully you'll see where this is going.

Detergents work on integral memb. proteins because they too are hydrophobic. They won't touch the peripheral ones because they are hydrophilic. The hydrophobicity is the important thing to consider here.

Hopre that is clear enough

Edited April 23, 2011 by D.Smalley

[SMF]

Peripheral proteins are removed first with high or low ionic strength or extreme pH solutions that disrupt their ionic bonds with the membrane. SM

[Fanghur]

Yes, thank you SMF, I understand that's the general practice for extracting peripheral proteins. But what I don't understand is why detergents couldn't be used as well, since they effectively destroy the structure of the membrane, presumably they could also remove the peripheral proteins as well, right?

[SMF]

Fanghur. SDS does its job by binding to hydrophobic elements of both lipids and integral proteins, and separating them into little soluble micelles. Most peripheral proteins are associated with the hydrophilic portion of integral proteins and could remain attached after detergent treatment depending on the nature of the association.SM