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Notes:
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The propensity of many proteins to oligomerize and associate to form complex structures from their constituent monomers,
is analyzed in terms of their hydrophobic (H), and electric pseudo-dipole (D) moment vectors. In both cases these vectors
are defined as the product of the distance between their positive and negative centroids, times the total hydrophobicity or
total positive charge of the protein. Changes in the magnitudes and directions of H and D are studied as monomers
associate to form larger complexes. We use these descriptors to study similarities and differences in two groups of
associations: a) open associations such as polymers with an undefined number of monomers (i.e. actin polymerization,
amyloid and HIV capsid assemblies); b) closed symmetrical associations of finite size, like spherical virus capsids and protein
cages. The tendency of the hydrophobic moments of the monomers in an association is to align in parallel arrangements
following a pattern similar to those of phospholipids in a membrane. Conversely, electric dipole moments of monomers
tend to align in antiparallel associations. The final conformation of a given assembly is a fine-tuned combination of these
forces, limited by steric constraints. This determines whether the association will be open (indetermined number of
monomers) or closed (fixed number of monomers). Any kinetic, binding or molecular peculiarities that characterize a
protein assembly, comply with the vector rules laid down in this paper. These findings are also independent of protein size
and shape.
This research was supported by grant BIO2013-48704-R from MCYT (Ministerio de Ciencia y Tecnología, Spain); from the Centre de Referència de R+D de Biotecnologia de la Generalitat de Catalunya and from the Comisión Coordinadora del Interior de Uruguay. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. |
