Fig. 10.

Truncation schemes applied to peptide sequence FHPEK from the IGPS HisH subunit. a) Hydrogen capping: the terminal ends are cut, and a single hydrogen is added to each end. b) Mixed capping: the peptide backbone atoms are removed from the terminal residues and the alpha carbons are capped, creating methyl groups, His and Glu are hydrogen capped at the N and C-terminus, respectively. c) Methyl capping: all peptide backbone atoms are removed from each residue and the alpha carbons methyl capped. d) Optimized geometries of each truncation scheme. The translucent red structure is the methyl capping scheme, the translucent blue is the mixed capping scheme, and the solid atom-colored model is the hydrogen capping scheme. The table shows O1 and O2 distances from the His δH resulting from different truncation schemes.