Correct Option: C

The most frequent and most regular of the domain structures are the alpha / beta domains. These domains consist of a central parallel or mixed beta-sheet surrounded by alpha-helix. All the glycolytic enzymes are alpha / beta structure proteins. There are three maim classes of alpha / beta structure proteins, TIM barrel, Rossman fold, and horseshoes fold (leucine-rich motif). The alpha/beta barrel fold is adopted by most enzymes performing a variety of catalytic reactions, but with very low sequence similarity. The cluster centers are found to occur in the middle of the strands or in the C-terminal of the strands. In most cases, the residues forming the clusters are part of the active site or are located close to the active site. The active site is majorly present at the carboxy-terminal side of the α sheets or the β strands.