Kinetic and structural evidence of the alkenal/one reductase specificity of human ζ-crystallin.
Human ζ-crystallin is a Zn(2+)-lacking medium-chain dehydrogenase/reductase (MDR) included in the quinone oxidoreductase (QOR) family because of its activity with quinones. In the present work a novel enzymatic activity was characterized: the double bond α,β-hydrogenation of medium-chain 2-alkenals and 3-alkenones. The enzyme is especially active with lipid peroxidation products such as 4-hydroxyhexenal, and a role in their detoxification is discussed. This specificity is novel in the QOR family, and it is similar to that described in the distantly related alkenal/one reductase family. Moreover, we report the X-ray structure of ζ-crystallin, which represents the first structure solved for a tetrameric Zn(2+)-lacking MDR, and which allowed the identification of the active-site lining residues. Docking simulations suggest a role for Tyr53 and Tyr59 in catalysis. The kinetics of Tyr53Phe and Tyr59Phe mutants support the implication of Tyr53 in binding/catalysis of alkenal/one substrates, while Tyr59 is involved in the recognition of 4-OH-alkenals.
Porté
Sergio
S
Department of Biochemistry and Molecular Biology, Faculty of Biosciences, Universitat Autònoma de Barcelona, Bellaterra, Spain.
Moeini
Agrin
A
Reche
Irene
I
Shafqat
Naeem
N
Oppermann
Udo
U
Farrés
Jaume
J
Parés
Xavier
X
D000447:Aldehydes / Q000378:metabolism; D002384:Catalysis; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D017931:DNA Primers / Q000235:genetics; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006865:Hydrogenation; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D013379:Substrate Specificity; D038226:zeta-Crystallins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*
D000447:Aldehydes; D017931:DNA Primers; D038226:zeta-Crystallins; C063409:4-hydroxyhexenal