  Despite recent breakthroughs in understanding how protein sequence relates to
structure and function, considerably less attention has been paid to the
general features of protein surfaces beyond those regions involved in binding
and catalysis. This paper provides a systematic survey of the universe of
protein surfaces and quantifies the sizes, shapes, and curvatures of the
positively/negatively charged and hydrophobic/hydrophilic surface patches as
well as correlations between such patches. It then compares these statistics
with the metrics characterizing nanoparticles functionalized with ligands
terminated with positively and negatively charged ligands. These particles are
of particular interest because they are also surface-patchy and have been shown
to exhibit both antibiotic and anticancer activities - via selective
interactions against various cellular structures - prompting loose analogies to
proteins. Our analyses support such analogies in several respects (e.g.,
patterns of charged protrusions and hydrophobic niches similar to those
observed in proteins), although there are also significant differences. Looking
forward, this work provides a blueprint for the rational design of synthetic
nanoobjects with further enhanced mimicry of proteins' surface properties.
