Multiple Choice
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 Kd 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.
-Which of the proteins mentioned in the passage has the highest isoelectric point?
A) WT BAZ2B
B) 10M+ BAZ2B
C) H3
D) H3K14ac
Correct Answer:

Verified
Correct Answer:
Verified
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