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Journal of Biochemistry Advance Access originally published online on January 29, 2007
Journal of Biochemistry 2007 141(4):489-493; doi:10.1093/jb/mvm049
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© 2007 The Japanese Biochemical Society.

Role of the Conserved Cysteine Residues of the 11.5 kDa Subunit in Complex I Catalytic Properties

Isabel Marques1,*, Alexandra V. Ushakova1, Margarida Duarte1 and Arnaldo Videira1,2

1IBMC – Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal; and 2ICBAS – Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Largo Prof. Abel Salazar 2, 4099-003 Porto, Portugal

*To whom correspondence should be addressed. Fax: +351-226099157, Email: imarques{at}ibmc.up.pt

Received November 29, 2006; Accepted January 23, 2007


  Abstract

Mitochondrial complex I exists as a mixture of two inter-convertible forms: active (A) and de-activated (D), the latter being sensitive to SH-modifying compounds. To investigate if the conserved cysteine-rich 11.5 kDa subunit of Neurospora crassa complex I is involved in this process, we subjected the corresponding genomic DNA to site-directed mutagenesis. The four cysteine residues of the subunit were separately substituted with serine residues and the resulting proteins were independently expressed in a null-mutant strain. All of the obtained mutant strains were able to assemble a complex I with similar kinetic properties to those observed in the wild-type enzyme, indicating that none of the cysteine residues of the 11.5 kDa protein is individually relevant for the A/D transition process. Diminished amounts of assembled complex I seem to be the major effect of these specific mutations. The cysteine residues are likely important to the acquisition and stabilization of the correct 11.5 kDa protein conformation and this is reflected in the assembly/stability of complex I.

Key Words: active/de-active transition, complex I, mitochondria, Neurospora crassa, site-directed mutagenesis


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