Secondary structure (helix / sheet / coil) is assigned live by 3Dmol.js from the actual 1UBQ coordinates, not looked up from a table. The Cα(i−1)–Cα(i+1) distance is measured directly off the crystal structure too — it's a rough proxy for how sharply the backbone bends at that point: shorter means a tighter turn. Position 10 is the one discussed above: it sits in a short, tight loop, and glycine — the only amino acid with no side chain — is what lets the backbone fold back on itself that sharply without two atoms crashing into each other. Try the other positions to see how much straighter (and less special) most of the chain looks by comparison.