Discovering subtype specific n-gram motifs in class C GPCR N-termini

G Protein-Coupled Receptors are a family of cell membrane proteins, whose class C is a current main target for drug development. Their primary sequences are studied as a source of information for the characterization of their behaviour. In previous research, different alignment-free sequence transformations were explored as the basis for the supervised discrimination of the various class C subtypes using Support Vector Machines. We also investigated an alignment-free sequence transformation based on n-gram protein motifs, under the hypothesis that the sequences' extra-cellular N-terminus domain could suffice to retain most of the subtype-discrimination capabilities of the complete receptor, and that a parsimonious selection of n-grams would be responsible for such classification success. In the current study, these previous results are extended by investigating a different classification procedure that now employs a subtype-vs-all the rest of subtypes approach, shifting towards the selection of those sequence motifs that distinguish each class C subtype from the rest. The reported results indicate the adequacy of this new approach, both in terms of discrimination ability and motif selection parsimony.