Passage
Interactions between positively charged histones and negatively charged nucleic acids are altered by acetylation and methylation of histone subunits. These different post-translational modifications are recognized by histone-binding proteins such as BROMO domain Adjacent to Zinc finger 2B (BAZ2B) . BAZ2B has a net negative charge but contains a lysine-rich regulatory region between its two histone-binding domains.NMR data revealed potential interactions between BAZ2B and histone subunit H3 (Figure 1) . Binding was confirmed by isothermal titration calorimetry (ITC) , which measures enthalpy of binding when a protein solution is titrated with ligand injections of equal volume and concentration. Each injection results in a negative peak as heat is released. Figure 2 shows ITC results when wild-type BAZ2B (WT) or BAZ2B with the regulatory region removed (10M+) were titrated with unmodified histone 3 (H3) or H3 that was acetylated at lysine-14 (H3K14ac) . In each case, the Hill coefficient was approximately 1.To test binding in a biological setting (in vivo) , WT and 10M+ BAZ2B were extracted from cell lysates on affinity columns containing H3 or H3K14ac covalently attached to beads. BAZ2B was then eluted and binding was quantified by Western blot (Figure 3) .
Figure 1 Electrostatic interactions between H3 and BAZ2B amino acid residues
Figure 2 ITC traces (A) and K_d values (B) of WT BAZ2B and 10M+ BAZ2B titrated with either unmodified H3 or H3Ka4ac
Figure 3 Western blot of BAZ2B recovered from unmodified or acetylated H3 columns
Adapted from Kostrhon S, Kontaxis G, Kaufmann T, et al. A histone-mimicking interdomain linker in a multidomain protein modulates multivalent histone binding. J Biol Chem. 2017;292(43) :17643-17657.
-Based on information in the passage, NMR data indicated electrostatic interactions involving all of the following amino acids EXCEPT:

Question

Passage
Interactions between positively charged histones and negatively charged nucleic acids are altered by acetylation and methylation of histone subunits. These different post-translational modifications are recognized by histone-binding proteins such as BROMO domain Adjacent to Zinc finger 2B (BAZ2B) . BAZ2B has a net negative charge but contains a lysine-rich regulatory region between its two histone-binding domains.NMR data revealed potential interactions between BAZ2B and histone subunit H3 (Figure 1) . Binding was confirmed by isothermal titration calorimetry (ITC) , which measures enthalpy of binding when a protein solution is titrated with ligand injections of equal volume and concentration. Each injection results in a negative peak as heat is released. Figure 2 shows ITC results when wild-type BAZ2B (WT) or BAZ2B with the regulatory region removed (10M+) were titrated with unmodified histone 3 (H3) or H3 that was acetylated at lysine-14 (H3K14ac) . In each case, the Hill coefficient was approximately 1.To test binding in a biological setting (in vivo) , WT and 10M+ BAZ2B were extracted from cell lysates on affinity columns containing H3 or H3K14ac covalently attached to beads. BAZ2B was then eluted and binding was quantified by Western blot (Figure 3) .

Figure 1 Electrostatic interactions between H3 and BAZ2B amino acid residues

Figure 2 ITC traces (A) and K_d values (B) of WT BAZ2B and 10M+ BAZ2B titrated with either unmodified H3 or H3Ka4ac

Figure 3 Western blot of BAZ2B recovered from unmodified or acetylated H3 columns
Adapted from Kostrhon S, Kontaxis G, Kaufmann T, et al. A histone-mimicking interdomain linker in a multidomain protein modulates multivalent histone binding. J Biol Chem. 2017;292(43) :17643-17657.
-Based on information in the passage, NMR data indicated electrostatic interactions involving all of the following amino acids EXCEPT:

Quizplus · Accepted Answer

11ecba2d_0eaa_028b_a3bf_118b5bd96a92_MD0008_00 All amino acids have a common backbone structure, but each has a unique side chain that determines its identity. The positively charged side chains of basic amino acids can interact electrostatically (ionic bonds) with the negatively charged side chains of acidic amino acids. These interactions can stabilize the tertiary structure of a protein as well as interactions between proteins. The passage states that NMR revealed potential electrostatic interactions between BAZ2B and H3, and the interactions are shown in Figure 1. This figure displays the side chains of the four amino acids involved in the interaction between BAZ2B and H3. The two positively charged amino acids in H3, lysine and arginine (Choices A and C), interact with the two negatively charged aspartate residues in BAZ2B (Choice B). Glutamate differs from aspartate in that it has an additional methylene (CH₂) unit before the carboxyl group in its side chain. Although glutamate is negatively charged and could potentially interact electrostatically with arginine or lysine, the data obtained from NMR do not show any glutamate residues involved in H3-BAZ2B interactions. Educational objective: Amino acids can be identified by their unique side chain structures. Positively charged amino acids such as lysine and arginine can interact with negatively charged amino acids such as aspartate and glutamate.

Passage Interactions Between Positively Charged Histones and Negatively Charged Nucleic Acids