Understanding the structure and function of catalases: clues from molecular evolution and in vitro mutagenesis

This review gives an overview about the structural organisation of differen t evolutionary lines of all enzymes capable of efficient dismutation of hyd rogen peroxide. Major potential applications in biotechnology and clinical medicine justify further investigations. According to structural and functi onal similarities catalases can be divided in three subgroups. Typical cata lases are homotetrameric haem proteins. The three-dimensional structure of six representatives has been resolved to atomic resolution. The central cor e of each subunit reveals a chracteristic "catalase fold", extremely well c onserved among this group. In the native tetramer structure pairs of subuni ts tightly interact via exchange of their N-terminal arms. This pseudo-knot structures implies a highly ordered assembly pathway. A minor subgroup ("l arge catalases") possesses an extra flavodoxin-like C-terminal domain. A gr eater than or equal to 25 Angstrom long channel leads from the enzyme surfa ce to the deeply buried active site. It enables rapid and selective diffusi on of the substrates to the active center. In several catalases NADPH is ti ghtly bound close to the surface. This cofactor may prevent and reverse the formation of compound II, an inactive reaction intermediate. Bifunctional catalase-peroxidases are haem proteins which probably arose via gene duplic ation of an ancestral peroxidase gene. No detailed structural information i s currently available. Even less is know about manganese catalases. Their d i-manganese reaction centers may be evolutionary related to manganese cente rs in photosystem II. Current research in this field focuses mainly on stre ss-regulation of catalase expression. on the role of catalases in plant def ense, and on in vivo and in vitro folding of catalases. (C) 1999 Elsevier S cience Ltd. All rights reserved.