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. Author manuscript; available in PMC: 2018 Feb 8.
Published in final edited form as: Biochemistry. 2016 Dec 30;56(2):391–402. doi: 10.1021/acs.biochem.6b00906

Figure 4.

Figure 4

E. coli YajL has a COOH--OOC H-bond with ambiguous protonation state. Panels A and B show the two independent Glu14-Asp23 H-bonds in the ASU. 2mFo-DFc electron density at 0.98 Å resolution contoured at 1.0σ (blue) and 5.3σ (purple) and mFo-DFc electron density contoured at 2.5σ (green). Primes indicate residues contributed by the other protomer, whose carbon atoms are colored grey. The modeled hydrogen atom on Glu14 is shown in white in each panel and agrees closely with the location of a mFo-DFc electron density peak. However, bond length analysis indicates both Glu14 and Asp23 are protonated, which is supported by the continuous 2mFo-DFc electron density for C=O bonds and broken density for C-O bonds in both instances.