= Aspartic acid
<Aspartic acid> is an alpha-<amino acid> with two <carboxyl groups>, represented in a neutral structural form as $\mathrm{HOOC{-}CH(NH_2){-}CH_2{-}COOH}$. Its <molecular formula> is $\mathrm{C_4H_7NO_4}$. One carboxyl group belongs to the amino-acid backbone and the other terminates the side chain.<Aspartic acid in ChEBI>[CHEBI:22660, Definition, Formula and structure]{ref}
The protein-associated L configuration and the sequence symbols Asp and D are separate naming conventions. A one-letter D in a protein sequence denotes the aspartic-acid residue; it is not a declaration of D stereochemistry.<Nomenclature and Symbolism for Amino Acids and Peptides (Recommendations 1983) by IUPAC-IUB Joint Commission on Biochemical Nomenclature>[3AA-1 amino-acid symbols; 3AA-3 stereochemistry]{ref}
Loss or redistribution of protons changes the ionic form. The name <aspartate> commonly denotes the anionic form. For example, a form with two carboxylates carrying $-1$ each and an ammonium group carrying $+1$ has net charge $-1-1+1=-1$. This charge count must be kept distinct from the L/D configuration and from atom connectivity.
The side-chain carboxyl chemistry also matters in <aspartic proteases>, where appropriately positioned acidic groups participate in <peptide bond> <hydrolysis>. Presence of an aspartic-acid residue alone does not establish catalytic activity: its geometry and chemical environment matter.<MEROPS glossary>[Catalytic Type, aspartic residues and activated water]{ref}
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