Triple-helical structures of (Pro-Hyp-Gly)n (n = 10, 11) at 100 K and room temperature (RT) were analyzed at 1.26 A resolution by using synchrotron radiation data. Totals of 49 and 42 water molecules per seven triplets in an asymmetric unit were found for the structures at 100 K and RT, respectively. These water molecules were classified into two groups, those in the first and second hydration shells. Although there was no significant difference between water molecules in the first shell at 100 K and those at RT, a significant difference between those in the second shell was observed. That is, the number of water molecules at RT decreased to one half and the average distance from peptide chains at RT became longer by about 0.3 A. On the other hand, of seven triplets in an asymmetric unit, three proline residues at the X position at 100 K clearly showed an up-puckering conformation, as opposed to the recent propensity-based hypothesis for the stabilization and destabilization of triple-helical structures by proline hydroxylation. This puckering was attributed to the interaction between proline rings and the surrounding water molecules at 100 K, which is much weaker at RT, as shown by longer average distance from peptide chains.

The original article to which this Erratum refers was published in

Since the 7/2-helical model was proposed by our group in 1977 based on the structure of (Pro-Pro-Gly)10, the single crystal structures of model peptides have contributed to obtain important information on the triple-helical structure of collagen. In this study, we report the high resolution crystal structure of collagen model peptide, (Pro-Hyp-Gly)11 using synchrotron diffraction data (SPring-8) at 100K. The structure has been refined to an R-factor of 0.15 and an Rfree-factor of 0.19 using 1960 and 217 reflections respectively, extending up to 1.5 Å resolution on the layer lines based on the repeating period of 20 Å. Different from (Pro-Hyp-Gly)10 case, only a few satellite spots were observed above and below the strong reflections on the 20 Å layer lines. The obtained molecular conformation and hydrogen bonding schemes of peptide chain are essentially the same as those found in the previous analyses of (Pro-Pro-Gly)n (n=9,10) and (Pro-Hyp-Gly)10, which suggests that the peptide molecule in this crystal takes the 7/2-helical conformation. Compared with that of (Pro-Hyp-Gly)10 case where intensity data were collected at room temperature, a fairly large number of water molecules bound to the triple-helical structure were found in this analysis. Most of the newly found water molecules maybe attributed to the data collection temperature together with the analysis at high resolution. All the proline rings of Hyp were found to be up-puckering, while those of Pro showed both up-and down-puckering.

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