Aspartate

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Standard codons for D : GAC GAT

Substitution preferences:
All protein types:
Favoured Glu ( 2) Asn ( 1)
Neutral Ser ( 0) Gln ( 0)
Disfavoured Gly (-1) His (-1) Lys (-1) Pro (-1) Thr (-1) Ala (-2) Arg (-2) Phe (-3)
Met (-3) Val (-3) Ile (-3) Tyr (-3) Cys (-3) Leu (-4) Trp (-4)

Intracellular proteins:
Favoured Glu ( 1) Asn ( 1)
Neutral Thr ( 0) Lys ( 0) Gly ( 0) His ( 0) Pro ( 0) Gln ( 0) Arg ( 0) Ser ( 0)
Disfavoured Ala (-1) Cys (-2) Val (-2) Trp (-2) Tyr (-2) Met (-2) Ile (-3) Leu (-3)
Phe (-3)

Extracellular proteins:
Favoured Asn ( 1)
Neutral Thr ( 0) Glu ( 0) Lys ( 0) Gly ( 0) His ( 0) Pro ( 0) Gln ( 0) Arg ( 0)
Ser ( 0)
Disfavoured Ala (-1) Val (-1) Met (-2) Leu (-2) Phe (-2) Ile (-2) Tyr (-2) Trp (-3)
Cys (-7)

Membrane proteins:
Favoured Glu ( 8) Asn ( 6) His ( 3) Lys ( 3) Gly ( 2) Gln ( 2) Arg ( 1)
Neutral Thr ( 0) Ala ( 0) Ser ( 0)
Disfavoured Tyr (-2) Pro (-2) Cys (-3) Ile (-3) Val (-3) Met (-3) Trp (-4) Leu (-5)
Phe (-6)

Substitutions: Aspartate (or Aspartic acid) is a negatively charged, polar amino acid. It thus most prefers to substitute for the other negatively charged (and very similar) amino acid Glutamate, though it can also substitute with other polar amino acids, in particular Asparginine, which differs only in that it contains an amino group in place of one of the oxygens found in Asparate (and thus also lacks a negative charge).

Role in structure: Being charged and polar, Asparates prefer generally to be on the surface of proteins, exposed to an aqueous environment. When buried within the protein, Aspartates (and Glutamtes) are frequently involved in salt-bridges, where they pair with a positively charged amino acid (such as Arginine shown below) to create stabilising hydrogen bonds, that can be important for protein stability.

Role in function: Aspartates are quite frequently involved in protein active or binding sites. The negative charge means that they can interact with positively charged non-protein atoms, such as cations like zinc.

Aspartate has a shorter side-chain than the very similar Glutamate meaning that is slightly more rigid within protein structures. This gives it a slightly stronger preference to be involved in protein active sites. Probably the most famous example of Asparate being involved in an active site is found within Serine proteases such as Trypsin, where it functions in the classical Asp-His-Ser catalytic triad:

In this context, it is quite rare to see Asparate exchange for Glutamate, though it is possible for Glutamate to play a simliar role.

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Please cite: M.J. Betts, R.B. Russell. Amino acid properties and consequences of subsitutions.
In Bioinformatics for Geneticists, M.R. Barnes, I.C. Gray eds, Wiley, 2003..