STRUCTURE OF HUMAN CHI-CHI ALCOHOL-DEHYDROGENASE - A GLUTATHIONE-DEPENDENT FORMALDEHYDE DEHYDROGENASE

The crystal structure of the human class III chi chi alcohol dehydroge nase (ADH) in a binary complex with NAD(+gamma) was solved to 2.7 Angs trom resolution by molecular replacement with human class I beta(1) be ta(1) ADH. chi chi ADH catalyzes the oxidation of long-chain alcohols such as omega-hydroxy fatty acids as well as S-hydroxymethyl-glutathio ne, a spontaneous adduct between formaldehyde and glutathione. There a re two subunits per asymmetric unit in the chi chi ADH structure. Both subunits display a semi-open conformation of the catalytic domain. Th is conformation is half-way between the open and closed conformations described for the horse EE ADH enzyme. The semi-open conformation and key changes in elements of secondary structure provide a structural ba sis for the ability of chi chi ADH to bind S-hydroxymethyl-glutathione and 10-hydroxydecanoate. Direct coordination of the catalytic zinc io n by Glu68 creates a novel environment for the catalytic zinc ion in c hi chi ADH. This new configuration of the catalytic zinc is similar to an intermediate for horse EE ADH proposed through theoretical computa tions and is consistent with the spectroscopic data of the Co(II)-subs tituted chi chi enzyme. The position for residue His47 in the chi chi ADH structure suggests His47 may function both as a catalytic base for proton transfer and in the binding of the adenosine phosphate of NAD( H). Modeling of substrate binding to this enzyme structure is consiste nt with prior mutagenesis data which showed that both Asp57 and Arg115 contribute to glutathione binding and that Arg115 contributes to the binding of omega-hydroxy fatty acids and identifies additional residue s which may contribute to substrate binding. (C) 1997 Academic Press L imited