252 Evolution of function in (b/a)8-barrel enzymes John A Gerltà and Frank M Raushely The (b/a)8-barrel is the most common fold in structurally closed, parallel b-sheet structure of the (b/a)8-barrel is characterized enzymes. Whether the functionally diverse formed from eight parallel (b/a)-units linked by hydrogen enzymes that share this fold are the products of either divergent bonds that form a cylindrical core. Despite its eightfold or convergent evolution (or both) is an unresolved question that pseudosymmetry, the packing within the interior of the will probably be answered as the sequence databases continue barrel is better described as four (b/a)2-subdomains in to expand. Recent work has examined natural, designed, and which distinct hydrophobic cores are located between the directed evolution of function in several superfamilies of (b/a)8- b-sheets and flanking a-helices [2]. barrel containing enzymes. The active sites are located at the C-terminal ends of the Addresses b-strands. So placed, the functional groups surround the ÃDepartments of Biochemistry and Chemistry, University of Illinois at active site and are structurally independent: the ‘old’ and Urbana-Champaign, 600 South Mathews Avenue, Urbana, ‘new’ enzymes retain functional groups at the ends of Illinois 61801, USA e-mail:
[email protected] some b-strands, but others are altered to allow the ‘new’ yDepartment of Chemistry, Texas A&M University, PO Box 30012, activity [3]. With this blueprint, the (b/a)8-barrel is opti- College Station, Texas 77842-3012, USA mized for evolution of new functions.