Glutamine

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Standard codons for Q : CAA CAG

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

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

Extracellular proteins:
Favoured
Neutral Pro ( 0) Asp ( 0) Glu ( 0) Asn ( 0) Gly ( 0) His ( 0) Met ( 0) Lys ( 0)
Arg ( 0) Ser ( 0) Thr ( 0) Val ( 0) Ala ( 0)
Disfavoured Leu (-1) Trp (-1) Tyr (-1) Ile (-1) Phe (-2) Cys (-5)

Membrane proteins:
Favoured His ( 7) Glu ( 7) Lys ( 6) Arg ( 5) Asn ( 3) Asp ( 2)
Neutral Pro ( 0) Tyr ( 0) Trp ( 0)
Disfavoured Ser (-1) Ala (-2) Met (-2) Gly (-2) Thr (-2) Leu (-2) Cys (-3) Val (-4)
Phe (-4) Ile (-4)

Substitutions: Glutamine is a polar amino acid. It thus most prefers to substitute for other polar residues, in particular Glutamate, which differs only in that it contains an oxygen in place of the amino group in Glutamine. It can also substitute with other polar amino acids.

Role in structure: Being polar, Glutamine prefers generally to be on the surface of proteins, exposed to an aqueous environment.

Role in function: Glutamines are quite frequently involved in protein active or binding sites. The polar side-chain is good for interactions with other polar or charged atoms.

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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..