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Are hinge residues more likely to occur on the surface?
To support our argument that hinge residues are hypermutable partly because they occur
on the surface, we quantified the degree to which the latter is the case. To do this, we
used a solvent accessible surface area (ASA) calculation program [53, 54] with a probe
radius of 1.4Å. The ASA of each of the backbone heavy atoms (amide nitrogen, α-
carbon, carbonyl carbon and oxygen) was calculated and summed for each residue in
each protein in the Hinge Atlas. We then binned the residues by this quantity. Lastly, we
counted the number of hinge residues in each bin and calculated HI and p-value as
before. As expected, bin #1 (containing the 20% of residues with highest ASA) was
significantly enriched with hinges (Figure 2.7; Table 2.6). Bin #2 was also highly
enriched, while bins #4 and #5 had fewer hinges, all with extremely high significance.
How many hinge sites appear in each protein?
Perhaps the simplest hinge consists of a single point on the chain separating two rigid
regions. However it is also possible for the chain to pass multiple times through the same
region, or to have multiple independent hinge regions. This leads to the question, how
many proteins had single hinge points, versus a larger number of hinge points? We
answer this question in Table 2.7. Most morphs had three or fewer hinge points.
Can hinges be predicted by a simple GOR-like method?
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