  Proteins belonging to immunoglobulin superfamily(IgSF) show remarkably
conserved nature both in their folded structure and in their folding process,
but they neither originate from very similar sequences nor demonstrate
functional conservation. Treating proteins as fractal objects, without studying
spatial conservation in positioning of particular residues in IgSF, this work
probed the roots structural invariance of immunoglobulins(Ig). Symmetry in
distribution of mass, hydrophobicity, polarizability recorded very similar
extents in Ig and in structurally-closest non-Ig structures. They registered
similar symmetries in dipole-dipole, {\pi}-{\pi}, cation-{\pi} cloud
interactions and also in distribution of active chiral centers, charged
residues and hydrophobic residues. But in contrast to non-Ig proteins, extents
of residual interaction symmetries in Ig.s of largely varying sizes are found
to converge to exactly same magnitude of correlation dimension - these are
named 'structural attractors', who's weightages depend on ensuring exact
convergence of pairwise-interaction symmetries to attractor magnitude. Small
basin of attraction for Ig attractors explained the strict and consistent
quality control in ensuring stability and functionality of IgSF proteins. Low
dependency of attractor weightage on attractor magnitude demonstrated that
residual-interaction symmetry with less pervasive nature can also be crucial in
ensuring Ig stability.
