Which statement best describes the localization and attachment of GPI-anchored proteins in the plasma membrane?
Solution
Correct Answer: Option A
The correct answer is: They are peripheral proteins attached to the outer leaflet of the plasma membrane.
GPI-anchored proteins (Glycosylphosphatidylinositol-anchored proteins) are a unique class of membrane-associated proteins. Instead of spanning the membrane or residing in the cytoplasm, they are covalently attached to a glycolipid anchor called GPI, which is embedded in the outer leaflet of the plasma membrane.
This means:
- They do not have transmembrane domains, distinguishing them from integral membrane proteins.
- The GPI anchor inserts into the lipid bilayer on the extracellular side (outer leaflet), thereby tethering the protein to the membrane.
- Because they are linked via a lipid anchor rather than a peptide spanning the membrane, GPI-anchored proteins are considered peripheral membrane proteins rather than integral ones.
- This anchorage allows GPI-anchored proteins mobility within the membrane and involvement in diverse functions such as enzymatic activity, cell adhesion, and signal transduction.
In contrast, peripheral proteins attached to the inner leaflet are usually connected to cytoskeletal elements or signaling molecules, and integral transmembrane proteins span the entire lipid bilayer.
Key points:
- GPI anchors tether proteins to the extracellular side (outer leaflet) of the plasma membrane.
- GPI-anchored proteins are peripheral proteins, not integral transmembrane proteins.
- They play important roles in cell signaling, adhesion, and enzymatic functions.
Reference: Alberts, B. et al., Molecular Biology of the Cell, 6th Edition, Chapter 10: Intracellular Compartments and Protein Sorting
GPI-anchored proteins (Glycosylphosphatidylinositol-anchored proteins) are a unique class of membrane-associated proteins. Instead of spanning the membrane or residing in the cytoplasm, they are covalently attached to a glycolipid anchor called GPI, which is embedded in the outer leaflet of the plasma membrane.
This means:
- They do not have transmembrane domains, distinguishing them from integral membrane proteins.
- The GPI anchor inserts into the lipid bilayer on the extracellular side (outer leaflet), thereby tethering the protein to the membrane.
- Because they are linked via a lipid anchor rather than a peptide spanning the membrane, GPI-anchored proteins are considered peripheral membrane proteins rather than integral ones.
- This anchorage allows GPI-anchored proteins mobility within the membrane and involvement in diverse functions such as enzymatic activity, cell adhesion, and signal transduction.
In contrast, peripheral proteins attached to the inner leaflet are usually connected to cytoskeletal elements or signaling molecules, and integral transmembrane proteins span the entire lipid bilayer.
Key points:
- GPI anchors tether proteins to the extracellular side (outer leaflet) of the plasma membrane.
- GPI-anchored proteins are peripheral proteins, not integral transmembrane proteins.
- They play important roles in cell signaling, adhesion, and enzymatic functions.
Reference: Alberts, B. et al., Molecular Biology of the Cell, 6th Edition, Chapter 10: Intracellular Compartments and Protein Sorting
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