Mechanisms of protection against irreversible oxidation of the catalytic cysteine of ALDH enzymes: Possible role of vicinal cysteines
Por:
Muñoz-Clares R.A., González-Segura L., Murillo-Melo D.S., Riveros-Rosas H.
Publicada:
1 oct 2017
Resumen:
The catalytic mechanism of the NAD(P)(+)-dependent aldehyde
dehydrogenases (ALDHs) involves the nucleophilic attack of the essential
cysteine (Cys302, mature HsALDH2 numbering) on the aldehyde substrate.
Although oxidation of Cys302 will inactivate these enzymes, it is not
yet well understood how this oxidation is prevented. In this work we
explore possible mechanisms of protection by systematically analyzing
the reported three-dimensional structures and amino acid sequences of
the enzymes of the ALDH superfamily. Specifically, we considered the
Cys302 conformational space, the structure and residues conservation of
the catalytic loop where Cys302 is located, the observed oxidation
states of Cys302, the ability of physiological reductants to revert its
oxidation, and the presence of vicinal Cys in the catalytic loop. Our
analyses suggested that: 1) In the apo-enzyme, the thiol group of Cys302
is quite resistant to oxidation by ambient O-2 or mild oxidative
conditions, because the protein environment promotes its high pK(a). 2)
NAD(P)(+) bound in the ``hydride transfer'' conformation afforded
total protection against Cys302 oxidation by an unknown mechanism. 3) If
formed, the Cys302-sulfenic acid is protected against irreversible
oxidation. 4) Of the physiological reductant agents, the dithiol lipoic
acid could reduce a sulfenic or a disulfide bond in the ALDHs active
site; glutathione cannot because its thiol group cannot reach Cys302,
and other physiological monothiols may be ineffective in those ALDHs
where their active site cannot sterically accommodate two molecules of
the monothiols. 5) Formation of the disulfides Cys301-Cys302,
Cys302-Cys304, Cys302-Cys305 and Cys-302-Cys306 in those ALDHs that have
these Cys residues is not probable, because of the permitted Cys
conformers as well as the conserved structure and low flexibility of the
catalytic loop. 6) Only in some ALDH2, ALDH9, ALDH16 and ALDH23 enzymes,
Cys303, alone or in conjunction with Cys301, allows disulfide formation.
Interestingly, several of these enzymes are mitochondrial. (C) 2017
Elsevier B.V. All rights reserved.
Filiaciones:
Muñoz-Clares R.A.:
Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad de México, 04510, Mexico
González-Segura L.:
Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad de México, 04510, Mexico
Murillo-Melo D.S.:
Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad de México, 04510, Mexico
Riveros-Rosas H.:
Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, México D. F., 04510, Mexico
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