Two disulfide bridges in the supplied crambin structure, Cys3-Cys40 and Cys4-Cys32, lie close enough together to compare directly. Calculate both SG-SG distances. Is the difference between them large or small relative to the typical covalent S-S single-bond length (about 2.0-2.1 angstrom)? Crambin packs three disulfide bonds into only 46 residues; does a small, chemically ordinary difference between these two bond lengths support or undermine describing all three as genuine stabilizing covalent crosslinks?

Coordinates are in angstrom (1 nm = 10 angstrom). XYZ atom rows are one-based after the two header lines. Use the supplied coordinate snapshot without optimization or periodic wrapping. Use S0007: the 6 Cys SG sites of 1CRN chain A, in residue order 3, 4, 16, 26, 32, 40 (rows 1-6 respectively). Row 1 = Cys3 SG; row 6 = Cys40 SG; row 2 = Cys4 SG; row 5 = Cys32 SG. Report both distances in angstrom to three decimals and answer the qualitative questions in words.

6
PDB 1CRN crambin, 6 Cys SG (disulfide sulfur) sites in residue order 3,4,16,26,32,40, chain A, model 1; angstrom
S 15.885 12.426 10.016
S 9.837 8.018 8.904
S 2.559 9.014 1.649
S 4.349 9.794 1.022
S 8.048 8.987 8.881
S 17.199 10.929 10.237


Attachments:
S0007: item-0002-asset-1.xyz