  Proteins appear to be the most dramatic natural example of self-organized
criticality (SOC), a concept that explains many otherwise apparently unlikely
phenomena. Protein conformational functionality is often dominated by
long-range hydro(phobic/philic) interactions which both drive protein
compaction and mediate protein-protein interactions. Superfamily transmembrane
GPCR are the largest family of proteins in the human genome; their amino acid
sequences form the largest data base for protein-membrane interactions. While
there are now structural data on the heptad transmembrane structures of
representatives of several heptad families, here we show that fresh insights
into global and some local chemical trends in GPCR properties can be obtained
accurately from sequences alone, especially by separating the extracellular and
cytoplasmic loops from transmembrane segments. The global mediation of
long-range water-protein interactions occurs in conjunction with modulation of
these interactions by roughened interfaces. Hydropathic roughening profiles are
defined here solely in terms of amino acid sequences, and knowledge of protein
coordinates is not required. Roughening profiles both for GPCR and some simpler
protein families display accurate and transparent connections to protein
functionality.
