There are four amino acids in this class, as shown below. Their side chains
consist of non-polar methyl- or methylene-groups. These amino acids are
usually located on the interior of the protein as they are hydrophobic
in nature. As can be seen, all of these side chains except for alanine
are bifurcated. In the cases of Val and Ile the bifurcation is close to
the main chain and can therefore restrict the conformation of the polypeptide
by steric hindrance. In the below diagram the red and blue atoms represent
polar main chain groups. Here is a pdb-file for
RasMol.
Hydrophobic-aromatic
Of the three residues in this class (see below) only phenylalanine is entirely
non-polar. Tyrosine's phenolic side chain has a hydroxyl substituent and
tryptophan has a nitrogen atom in its indole ring sytem. These residues
are nearly always found to be largely buried in the hydrophobic interior
of a proteins as they are prdeominantly non-polar in nature. However, the
polar atoms of tyrosine and tryptophan allow hydrogen bonding interactions
to be made with other residues or even solvent molecules. Here is a
pdb-file
for RasMol.
Index
to Course Material
Index
to Section 2
Page
3
