Low-resolution X-ray diffraction analysis of a protein composed of long stretches ofthe sequence(-Gly-Ser-Gly-Ala-Gly-Ala-)n, where n indicates any number of repeats,shows an extended structure of stacked layers, with a repeat distance between layersthat alternates between 3.5 Å and 5.7 Å. Propose a mođel that explains this scenario.5. The right-hand panel in the linked figure shows sedimentation equilibriumanalytical ultracentrifugation data for a mixture containing equimolar amounts oftwo fibrous proteins, Vps27 and Hsel. The blue circles are the data and the blackline is the expected plot for a monodisperse 1:1 Vps27:Hsel complex of 23.7 kDa. Inthe left-hand panel, data is shown for Vps27 alone. The black line represents theexpected curve for monomeric Vps27. Both experiments were run under identicalconditions (same buffer, same spinning speed etc.) and the proteins have the samepartial specific volume.

Fibroins are insoluble proteins that are present in silk produced by insects, such as the larvae of…

Answered: Low-resolution X-ray diffraction…

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter31: Completing The Protein Life Cycle: Folding, Processing, And Degradation

Section: Chapter Questions

Problem 20P

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Remembering that the amino acid side chains projecting from each polypeptide backbone in a β sheet point alternately above and below the plane of the sheet, consider the following protein sequence: Leu-Lys-Val-Asp-Ile-Ser-Leu-Arg- Leu-Lys-Ile-Arg-Phe-Glu. Do you find anything remarkable about the arrangement of the amino acids in this sequence when incorporated into a β sheet? Can you make any predictions as to how the β sheet might be arranged in a protein?
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?
Approximate molecular weight for an unknown protein from gel-filtration experiment is 130 kDa. Thirty six mg of this pure protein was treated with excess of fluorodinitrobenzene. After the reaction and complete acid hydrolysis the mixture was found to contain 356 µg of dinitrobenzene derivative of methionine (free acid) and no other amino acid-dinitrobenzene derivatives. Is this protein consisting of single polypeptide chain or multiple subunits? If it consists of multiple subunits, then how many? From these data, can you calculate the molecular weight of the protein more precisely?
Three peptides were obtained from a trypsin digestion of two different polypeptides. indicate the possible sequences from the given data and tell what further experiment should be carried out in order to determine the primary structure of the polypeptide. Polypeptide II: 1. Val-Leu-Gly-Glu 2. Ala-Glu-Pro-Arg 3. Ala-Met-Gly-Lys
. Disulfide bonds have been shown to stabilize proteins (i.e., make them less likely to unfold). Consider the cases shown schematically below for two variants of the same protein. In case #1 the disulfide forms between Cys residues that have been introduced near the protein N- and C-termini, and in case #2 the disulfide forms between Cys residues that have been introduced in the middle of the protein sequence. Which protein is likely to be more stable? (Note: Assume the disulfide bond is intact in both the unfolded and folded states). Explain your reasoning.
Polylysine adopts a random structure in solution at physiological pH (i.e. 7.4). Given that the e-amino group of lysine has a pKa of 10.5, under what circumstances do you think polylysine will form an a-helix? Give an explanation for your decision. Given the pKa of the side-chain COOH group, under what circumstances would you anticipate polyglutamate to form an a-helix?
GT 3 A. Write the structure of the pentapeptide GLDSC. B. What is the complete name of this pentapeptide? Show a tertiary structure of ACGGC after a disulfide bond forms. A sample of an unknown peptide was divided into two aliquots. One aliquot was treated with trypsin; the other was treated with cyanogen bromide. Given the following sequences (N-terminal to C- terminal) of the resulting fragments, deduce the sequence of the original peptide. Trypsin treatment Asn-Thr-Trp-Met-lle-Lys Gly-Tyr-Met-Gln-Phe Val-Leu-Gly-Met-Ser-Arg Cyanogen bromide treatment Gln-Phe Val-Leu-Gly-Met lle-Lys-Gly-Tyr-Met Ser-Arg-Asn-Thr-Trp-Met
At physiological pH (i.e. 7.4), polylysine assumes a random structure in solution. Given that the pKa for the e-amino group of lysine is 10.5, under what conditions would you expect polylysine to form an a-helix? Explain your reasoning. Under what conditions would you expect polyglutamate to form an a-helix, given that the pKa for the side-chain COOH group is 4.3?
Both hsp60-like and hsp70 molecular chaperonesshare an affinity for exposed hydrophobic patches on pro-teins, using them as indicators of incomplete folding. Whydo you suppose hydrophobic patches serve as critical sig-nals for the folding status of a protein?
Polyglycine, a simple polypeptide, can form a helix with φ = -80°, ψ = +150°. From the Ramachandran plot (as shown), describe this helix with respect to handedness.
Pectin, which occurs in plant cell walls, exist in nature as a polymer of D-galacturonic acid methylated at carbon 6 of the monomer. Draw a haworth projection for a repeating disaccharide unit of pectin with one methylated and one unmethylated monomer unit in a (1-->4) linkage
2. Glycine, proline, and serine residues are rarely found in α helices. Explain why this is the case. Why is it the case that glycines are highly conserved in the evolution of proteins?

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