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Biochemistry

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Predicting Integral Protein Structure Using a Hydropathy Plot

BIOCHM-89L4AU

By plotting the average hydrophobicity of the amino acids in a protein sequence from the amino- to carboxyl-terminus using a sliding window (e.g., every 10 amino acids), one can predict the occurrence of transmembrane alpha-helix spanning regions, requiring about 20 amino acids.

A hypothetical, integral erythrocyte protein was purified, sequenced and its hydropathy index plotted as shown below revealing, at least, one transmembrane alpha-helix. In addition, when intact erythrocytes were treated with the impermeant protease trypsin, a heavily glycosylated N-terminal end was released, whereas no C-terminal fragment was released.

Use your understanding of protein hydropathy plots and the structure and biochemical nature of biological membranes to determine which of the following statements BEST describes the protein illustrated here.

M. Rumpho-Kennedy. Created for Albert.io. Copyright 2016. All rights reserved.

A

The protein is likely to span the membrane one time using amino acids 65-85, the N-terminus is exposed extracellularly, and the C-terminus is imbedded in the lipid bilayer.

B

The protein is likely to span the membrane three times using amino acids 15-35, 40-65, and 85-110, the N-terminus is exposed extracellularly, and the C-terminus extends into the interior of the cell (intracellular).

C

The protein is likely to span the membrane four times using amino acids 15-35, 40-65, 65-85 and 85-110; the N-terminus is extracellular and the C-terminus extends intracellularly.

D

The protein is likely to span the membrane one time using amino acids 65-85, the N-terminus is exposed extracellularly, and the C-terminus extends intracellularly.