1. Abbreviation: Pro.
2. One-letter code: P.
3. Molecular mass: 115 daltons.
4. Side-chain (or R-group) features:
   • Formula: -(CH₂)₃- (cyclic);
   • Category: Hydrophobic;
   • pK_a: none; (since the imino nitrogen is not part of the side-chain).

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