Questions deal with a transport protein found in the plasma membrane of certain
ID: 63325 • Letter: Q
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Questions deal with a transport protein found in the plasma membrane of certain epithelial cells that transports Cl- specifically across the plasma membrane of epithelial cells. The transport protein is relatively large, ~1500 amino acids (~200KDa). It has 12 transmembrane regions and most of the protein resides within the cytosol including its amino terminus. Less than 10% of the protein is exposed outside the cell. The protein lacks a canonical signal peptide. 1. Is the carboxyl terminus also located in the cytosol? Explain. 2. Draw a hydropathy plot that depicts the protein. 3. At what capacity if any does targeting require SRP activity since there is no signal peptide? Explain. Questions deal with a transport protein found in the plasma membrane of certain epithelial cells that transports Cl- specifically across the plasma membrane of epithelial cells. The transport protein is relatively large, ~1500 amino acids (~200KDa). It has 12 transmembrane regions and most of the protein resides within the cytosol including its amino terminus. Less than 10% of the protein is exposed outside the cell. The protein lacks a canonical signal peptide. 1. Is the carboxyl terminus also located in the cytosol? Explain. 2. Draw a hydropathy plot that depicts the protein. 3. At what capacity if any does targeting require SRP activity since there is no signal peptide? Explain. 1. Is the carboxyl terminus also located in the cytosol? Explain. 2. Draw a hydropathy plot that depicts the protein. 3. At what capacity if any does targeting require SRP activity since there is no signal peptide? Explain.Explanation / Answer
1) Yes, the carboxy terminal is also located in the cytosol. This is because the transport protein has 12 transmembrane regions with the amino terminus also being in the cytosol.
Since their are an even number of transmembrane segments, the carboxy and amino terminals are goin to be on the same side, in this case both are in the cytosol.
2) A hydropathy plot is a quantitative analysis of the degree of hydrophobicity or hydrophilicity of amino acids of a protein which is used to characterize or identify possible structure or domains of a protein.
However in this case, the hydropathy plot cannot be drawn because it needs the entire amino acid sequence of the protein. This data has not been provided with.
3) An SRP or Signal Recognition Particle is a cytosolic ribonucleoprotein which recognizes and targets nascent polypeptide into the ER of eukaryotes.
In this case, since the protein lacks a canonical signal peptide, it still interacts with the SRP because the action of the SRP in targeting the nascent polypeptide to the membrane of the ER is essential in ultimately translocating the protein to the plasma membrane.
Only polypeptides that have been targeted to the ER membrane can be translocated to the plasma membrane.
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