Amino acid repeat patterns in protein sequences: their diversity and structural-functional implications.

All the protein sequences from SWISS-PROT database were analyzed for occurrence of single amino acid repeats, tandem oligo-peptide repeats, and periodically conserved amino acids. Single amino acid repeats of glutamine, serine, glutamic acid, glycine, and alanine seem to be tolerated to a considerable extent in many proteins. Tandem oligo-peptide repeats of different types with varying levels of conservation were detected in several proteins and found to be conspicuous, particularly in structural and cell surface proteins. It appears that repeated sequence patterns may be a mechanism that provides regular arrays of spatial and functional groups, useful for structural packing or for one to one interactions with target molecules. To facilitate further explorations, a database of Tandem Repeats in Protein Sequences (TRIPS) has been developed and is available at URL: http://www.ncl-india.org/trips.