  This paper presents the methods that have participated in the SHREC 2021
contest on retrieval and classification of protein surfaces on the basis of
their geometry and physicochemical properties. The goal of the contest is to
assess the capability of different computational approaches to identify
different conformations of the same protein, or the presence of common
sub-parts, starting from a set of molecular surfaces. We addressed two
problems: defining the similarity solely based on the surface geometry or with
the inclusion of physicochemical information, such as electrostatic potential,
amino acid hydrophobicity, and the presence of hydrogen bond donors and
acceptors. Retrieval and classification performances, with respect to the
single protein or the existence of common sub-sequences, are analysed according
to a number of information retrieval indicators.
