Membrane-spanning proteins are notoriously difficult to characterize by x-ray crystallography.Hollonut of VISA Toplona. Explain how the information in the diagrams below can be used in the detection of membrane-spanning proteins consisting of alpha helices, given that the lipid portion of a typical bilayer isapproximately 30 Å thick.Amino terminus5.4 A(3.6 residues)b. Identify and briefly describe how the features of a transmembrane protein composed of ß-sheetsdiffer from that above.

The biological membranes consist of a bi-layer of phospholipid molecules.In addition, there membrane…

Answered: Membrane-spanning proteins are…

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter32: The Reception And Transmission Of Extracellular Information

Section: Chapter Questions

Problem 11P

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Describe the general structure of a type 2 alpha helix protein. Explain how type 2 alpha helix transmembrane domains can be used to form pathways for large polar and charged molecules to traverse the lipid bilayer of the cell membrane.
Which intermolecular forces are important in acetic acid, CH3 –(C=0)-oh? A particular amino acid contains a- CHNH3+ group. Is this amino acid more likely to be found on the inside or the outside of the folded protein? Briefly explain. The addition of ethanol, CH3CHOH, t an aqueous solution lowers the surface tension of the solution. Predict whether adding ethanol to an aqueous protein solution will tend to stabilize or unfold the protein. Briefly explain.
Bacteriorhodospin (Mw = 26 kDa) is a protein with purple colour. The protein acts as a light-activated proton pump that provides energy for cellular functions. The structure, revealed by both electron microscopy and X-ray crystallography, showed that the protein consists of 7 transmembrane spanning helices (TMH). Each TMH traverses the lipid bilayer completely (thickness of 45 Å). a)Calculate the minimum number of amino acid residues needed per TMH to completely cross the membrane. b)Estimate how large a fraction of the bacteriorhodopsin protein that is made up by TMHs. c)Now that you know the fraction of the protein that is made up by TMHs, at which ψ/φangles will the amino acids cluster in a Ramachandran plot?
The following are sequences from three different alpha helices found inhuman proteins: hBak(72-87): GQVGRQLAIIGDDINR hCB1(196-210): VTASFTASVGSLFLT hCB2(248-262): LVLAVLLICWFPVL Classify each of these three helices as either a) mostly hydrophobic, b)mostly hydrophilic, or c) amphipathic. Use the helical wheel to explainyour answers. Given the character of these helices, in which part of the protein wouldyou expect them to reside?
Peptides and small proteins fold spontaneously in aqueous solution at room temperature. Thus, for a small protein in water, we can say ΔG FOLD < 0. Denoting the unfolded protein as Unf and the folded protein as Fld, we can write the following equation:Unf(aq)--DELTA G FOLD----> Fld(aq)Considering the transition from the unfolded state (in which there are many possible conformations) to the folded state (only one conformation), there is clearly a decrease in the entropy of the protein. However, protein folding is (correctly) described as an entropically driven process.a) Resolve this apparent paradox by identifying the enthalpy (ΔH) and entropy (−TΔS)components involved in protein…
Many transmembrane proteins have a large series of hydrophobic amino acids such as those in the middle of the protein (around b). Why would this make sense, and where would you expect these to be located in the final protein structure?
The process of a protein folding from an inactive unfolded structure to theactive folded structure can be represented by the following equation: unfolded protein ⇌ folded proteinThe values of ΔH° and ΔS° for the folding of the protein lysozyme are: ΔH ° = -280 kJ/ mol ΔS ° = -790 J/mol • K(a) Calculate the value of ΔG° for the folding of lysozyme at 25 °C.(b) At what temperature would you expect the unfolding of lysozyme tobecome favorable? (c) At what temperature would the ratio of unfolded protein to foldedprotein be 1:5?
Transmembrane portrudes on both sides. Integral protein is in the width of the bilayer and may portrude on one or both sides of the bilayer. Is Transmembrane Protein semi-similar to Integral Proteins? How can we tell the difference of the two?
A protein molecule is approximately spherical and has a hydrodynamic diameter of35μm. What is the translational diffusion coefficient of the protein at 20°C in diluteaqueous solution?
Consider the phenolic hydroxyl group of a particular Tyr residue in a protein. Suppose the hydroxyl group in the unfolded protein in aqueous solution, where the group is exposed to H2O, has a pKa of 10.0. If that group is found in a hydrophobic environment in the interior of the protein when the protein is folded into its native tertiary structure, would you expect the pKa of the phenolic hydroxyl to be higher or lower in the folded protein interior than in H2O? Explain your reasoning.
Proteins may be bound to the exoplasmic or cytosolic face of the plasma membrane by way of covalently attached lip- ids. What are the three types of lipid anchors responsible for tethering proteins to the plasma membrane bilayer? Which type is used by cell surface proteins that face the external medium? By glycosylated proteoglycans?
a) Canonical forces in protein folding. Describe how these forces come into play when a protein folds. Why do are other intermolecular interactions important to fully understand folding processes?

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