The Amino Acids

1
The Amino Acids

• Self-assessment exercises

2
alanine (ala)

• R-group non-polar ambivalent
• Substrate for alanine transaminase (ALT)

3
aspartate (asp)

• R-group acidic (-) charge.
• Active site of aspartate proteases.
• Catalytic triad of serine proteases.
• Forms essential salt bridge with histidine 146 in
  T form of hemoglobin
• Substrate for aspartate transaminase (AST)

4
cysteine (cys)

• R-group polar sulfhydryl
• Forms disulfide crosslinks
• Crosslinks keratins (hair)
• Crosslinks procollagen monomers in register for
  trimer formation

5
glycine (gly)

• R-group hydrogen
• Smallest R-group
• Every third residue in collagen
• Mutations in collagen lead to osteogenesis
  imperfecta

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glutamate (glu)

• R-group acidic (-) charge
• Carboxylated to form gla by vitamin K mediated
  reactions in blood clotting.
• Mutated to valine in sickle cell hemoglobin

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asparagine (asn)

• R-group polar uncharged
• Substrate for N-linked glycosylation of proteins

8
threonine (thr)

• R-group non-polar ambivalent
• Substrate for phosphorylation (lecture 10)
• Substrate for O-linked glycosylation

9
isoleucine (ile)

• R-group non-polar

10
histidine (his)

• R-group weak base, reversible () charge
• Proximal and distal histidines in Hb
• Terminal histidine 146 mediates Bohr effect
• Serine protease catalytic triad

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lysine (lys)

• R-group basic () charge.
• Hydroxylated by lysyl hydroxylase in procollagen.
• Hydroxylysine is substrate for glycosylation.
• Oxidized to the aldehyde, allysine, in collagen
  fibril.
• Lysine forms Schiff bases with aldehydes,
  including allysine (collagen) and glucose (all
  proteins).

12
proline (pro)

• R-group polar uncharged
• Incompatible with a-helix
• Abundant in collagen helix
• Hydroxylated by prolyl hydroxylase to stabilize
  tropocollagen (trimer)

13
leucine (leu)

• R-group non-polar
• Common in heptad repeats (leucine zipper)

14
methionine (met)

• R-group non-polar hydrophobic

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phenylalanine (phe)

• R-group non-polar hydrophobic

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serine (ser)

• R-group polar
• Active site of serine proteases
• Substrate for phosphorylation

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tryptophan (trp)

• R-group the MOST hydrophobic

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valine (val)

• R-group hydrophobic
• Substitutes for glutamate in sickle cell
  hemoglobin

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tyrosine (tyr)

• R-group hydrophobic
• Substrate for phosphorylation (lecture 10)

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glutamine (gln)

• R-group polar
• Codon is CAG.
• Long tracks in polyglutamine diseases such as
  Huntington.

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arginine (arg)

• R-group polar uncharged