The human insulin receptor (IR) is an integral membrane protein that plays a cri
ID: 256106 • Letter: T
Question
The human insulin receptor (IR) is an integral membrane protein that plays a critical role in controlling glucose homeostasis. Recently, Li, et al. solved the structure of the IR transmembrane domain involved in signal transduction initiation. Below is the sequence of the transmembrane domain.
TYFYVTDYLDVPSNIAKIIIGPLIFVFLFSVVIGSIYLFLRKRQPDGPL
(a) Explain why this amino acid sequence is favorable for a transmembrane domain.
(b) Briefly describe the difference between integral, lipid-linked, and peripheral membrane proteins (one sentence each).
Explanation / Answer
A membrane protein may contain three regions: outer membrane region, transmembrane region, and inner membrane region. Outer and inner membrane regions are hydrophilic in nature. Transmembrane region is considered as hydrophobic . Therefore, membrane proteins broadly consist of hydrophobic and hydrophilic regions.
Hydrophobic amino acids are those with side chains that do not reside in water. Hence, these are mostly found in hydrophobic regions. Transmembrane regions often do not interact with water. The given sequence most of the hydrophobic amino acids such as F, A, V, I and P. the presence of these amino acids makes this sequence favorable to reside in transmembrane region.
Integral or intrinsic proteins are those that interact with the hydrophobic region of the phospholipid bilayer. They cannot be easily detached from the membrane.
Lipid-linked and peripheral proteins (extrinsic) are those that do not interact with hydrophobic regions. Rather they are bound to membrane by interacting with intrinsic proteins or to lipid polar head groups.
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