FUNCTIONALLY ESSENTIAL, INVARIANT GLUTAMATE NEAR THE C-TERMINUS OF STRAND BETA-5 IN VARIOUS (ALPHA BETA(8))-BARREL ENZYMES AS A POSSIBLE INDICATOR OF THEIR EVOLUTIONARY RELATEDNESS/

Twelve different (alpha/beta)(8)-barrel enzymes belonging to three str ucturally distinct families were found to contain, near the C-terminus of their strand beta 5, a conserved invariant glutamic acid residue t hat plays an important functional role in each of these enzymes, The s earch was based on the idea that a conserved sequence region of an (al pha/beta)(8)-barrel enzyme should be more or less conserved also in th e equivalent part of the structure of the other enzymes with this fold ing motif owing to their mutual evolutionary relatedness. For this pur pose, the sequence region around the well conserved fifth beta-strand of alpha-amylase containing catalytic glutamate (Glu230, Aspergillus o ryzae alpha-amylase numbering), was used as the sequence-structural te mplate. The isolated sequence stretches of the 12 (alpha/beta)(8)-barr els are discussed from both the sequence-structural and the evolutiona ry point of view, the invariant glutamate residue being proposed to be a joining feature of the studied group of enzymes remaining from thei r ancestral (alpha/beta)(8)-barrel.