PREPARATION AND PROPERTIES OF RECOMBINANT CORYNEBACTERIAL SARCOSINE OXIDASE - EVIDENCE FOR POSTTRANSLATIONAL MODIFICATION DURING TURNOVER WITH SARCOSINE

The genes encoding the four subunits of sarcosine oxidase from Corynebacterium sp. P-1 were isolated and overexpressed in a single step by using indicator plates to screen a genomic library for colonies that generated hydrogen peroxide in a sarcosine-dependent reaction. The genomic library was constructed by inserting size-fractionated genomic DNA, previously subjected to partial digestion by Sau3AI, into pBluescript II SK (+). At least 1.0 kb, but less than 4.0 kb, can be deleted from the 3' end of the original cornyebacterial insert (7.3 kb) without affecting sarcosine oxidase expression, consistent with the estimated 5.0-kb operon size. Recombinant sarcosine oxidase is isolated as a heterotetramer containing equimolar amounts of covalent and noncovalent flavin, identical to that observed for enzyme isolated from Corynebacterium sp. P-1. Despite its similar flavin content, recombinant enzyme exhibits significantly different spectral properties than enzyme from Corynebacterium sp. P-1 (values shown in parentheses) [epsilon450 = 9.7 (12.7) mM-1 cm-1; A368/A450 = 1.0 (0.83); A280/A450 = 16.9 (12.2)]. This difference is due to the fact that about half of the covalent flavin in recombinant enzyme forms a reversible covalent 4a-adduct with a cysteine residue (lambda(max) = 383 nm; epsilon383 = 7.3 mM-1 cm-1). The equilibrium is shifted in favor of adduct dissociation by oxidizing the cysteine residue with hydrogen peroxide or by alkylation with methyl methanethiosulfonate in a reaction that is fully reversible upon addition of excess dithiothreitol. The cysteine residue is also oxidized during aerobic turnover with sarcosine. Reaction of the cysteine residue with hydrogen peroxide (or a precursor) formed during turnover partially competes with the release of hydrogen peroxide into solution, as judged by the effect of catalase on this reaction. Although the same specific activity is observed for recombinant enzyme and enzyme from Corynebacterium sp. P-1, the recombinant enzyme exhibits a pronounced lag in an NADH peroxidase-coupled assay. The lag is eliminated by prior disruption of the 4a-thiolate adduct via reaction with hydrogen peroxide or methyl methane-thiosulfonate. The results show that the 4a-thiolate adduct is an inactive form of sarcosine oxidase that can be activated by reaction with sarcosine in what appears to be the first example of a posttranslational modification associated with turnover. Complete activation occurs in vivo when sarcosine oxidase is produced in Corynebacterium sp. P-1, where enzyme synthesis is induced by growth of the organism with sarcosine as the source of carbon and energy. The opportunity for in vivo activation is diminished when the recombinant enzyme is produced in Escherichia coli under the control of a vector-encoded lac promoter.