The covalent structure of the small subunit from Pseudomonas putida amine dehydrogenase reveals the presence of three novel types of internal cross-linkages, all involving cysteine in a thioether bond
I. Vandenberghe et al., The covalent structure of the small subunit from Pseudomonas putida amine dehydrogenase reveals the presence of three novel types of internal cross-linkages, all involving cysteine in a thioether bond, J BIOL CHEM, 276(46), 2001, pp. 42923-42931
Pseudomonas putida contains an amine dehydrogenase that is called a quinohe
moprotein as it contains a quinone and two hemes c as redox active groups.
Amino acid sequence analysis of the smallest (8.5 kDa), quinone-cofactor-be
aring subunit of this heterotrimeric enzyme encountered difficulties in the
interpretation of the results at several sites of the polypeptide chain. A
s this suggested posttranslational modifications of the subunit, the struct
ural genes for this enzyme were determined and mass spectrometric de novo s
equencing was applied to several peptides obtained by chemical or enzymatic
cleavage. In agreement with the interpretation of the X-ray electronic den
sities in the diffraction data for the holoenzyme, our results show that th
e polypeptide of the small subunit contains four intrachain cross-linkages
in which the sulfur atom of a cysteine residue is involved. Two of these cr
oss-linkages occur with the beta -carbon atom of an aspartic acid, one with
the gamma -carbon atom of a glutamic acid and the fourth with a tryptophan
quinone residue, this adduct constituting the enzyme's quinone cofactor, CT
Q. The thioether type bond in all four of these adducts has never been foun
d in other proteins. CTQ is a novel cofactor in the series of the recently
discovered quinone cofactors.