Indel PDB: A database of structural insertions and deletions derived from sequence alignments of closely related proteins

Background: Insertions and deletions (indels) represent a common type of sequence variations, which are less studied and pose many important biological questions. Recent research has shown that the presence of sizable indels in protein sequences may be indicative of protein essentiality and their role in protein interaction networks. Examples of utilization of indels for structure-based drug design have also been recently demonstrated. Nonetheless many structural and functional characteristics of indels remain less researched or unknown. Description: We have created a web- based resource, Indel PDB, representing a structural database of insertions/ deletions identified from the sequence alignments of highly similar proteins found in the Protein Data Bank (PDB). Indel PDB utilized large amounts of available structural information to characterize 1-, 2- and 3- dimensional features of indel sites. Indel PDB contains 117,266 non- redundant indel sites extracted from 11,294 indel- containing proteins. Unlike loop databases, Indel PDB features more indel sequences with secondary structures including alpha- helices and beta- sheets in addition to loops. The insertion fragments have been characterized by their sequences, lengths, locations, secondary structure composition, solvent accessibility, protein domain association and three dimensional structures. Conclusion: By utilizing the data available in Indel PDB, we have studied and presented here several sequence and structural features of indels. We anticipate that Indel PDB will not only enable future functional studies of indels, but will also assist protein modeling efforts and identification of indel- directed drug binding sites.