The evolutionary variability of a protein's residues is highly dependent on protein region and function. Solvent-exposed residues, excluding those at interaction interfaces, are more variable than buried residues whereas active site residues are considered to be conserved. The abovementioned rules apply also to α/β-hydrolase fold proteins-one of the oldest and the biggest superfamily of enzymes with buried active sites equipped with tunnels linking the reaction site with the exterior. We selected soluble epoxide hydrolases as representative of this family to conduct the first systematic study on the evolution of tunnels. We hypothesised that tunnels are lined by mostly conserved residues, and are equipped with a number of specific variable residues that are able to respond to evolutionary pressure. The hypothesis was confirmed, and we suggested a general and detailed way of the tunnels' evolution analysis based on entropy values calculated for tunnels' residues. We also found three different cases of entropy distribution among tunnel-lining residues. These observations can be applied for protein reengineering mimicking the natural evolution process. We propose a 'perforation' mechanism for new tunnels design via the merging of internal cavities or protein surface perforation. Based on the literature data, such a strategy of new tunnel design could significantly improve the enzyme's performance and can be applied widely for enzymes with buried active sites.

MOTIVATION: Tunnels, pores, channels, pockets and cavities contribute to proteins architecture and performance. However, analysis and characteristics of transportation pathways and internal binding cavities are performed separately. We aimed to provide universal tool for analysis of proteins integral interior with access to detailed information on the ligands transportation phenomena and binding preferences. RESULTS: AQUA-DUCT version 1.0 is a comprehensive method for macromolecules analysis from the intramolecular voids perspective using small ligands as molecular probes. This version gives insight into several properties of macromolecules and facilitates protein engineering and drug design by the combination of the tracking and local mapping approach to small ligands. AVAILABILITY AND IMPLEMENTATION: http://www.aquaduct.pl. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.