Which amino acid is important for collagen cross-linking?

• A. Alanine
• B. Proline
• C. Histidine
• D. Arginine

Answer: (B)

Collagen cross-linking depends on having a properly formed collagen structure so that reactive residues can pair up and form covalent links between molecules. Proline (and its hydroxylated form, hydroxyproline) is central to this because these residues give collagen its rigid, stable triple helix. When proline is hydroxylated, the helix becomes even more stable, and this stability allows lysine- and hydroxylysine-containing regions to align correctly for cross-links to form (a process involving enzymes like lysyl oxidase). Among the options, proline is the best fit because it underpins the structural integrity of collagen required for cross-linking; the other amino acids listed don’t play that specific structural role in enabling collagen cross-links.