Biochemical and spectroscopic characterization of purified Latex Clearing Protein (Lcp) from newly isolated rubber degrading Rhodococcus rhodochrous strain RPK1 reveals novel properties of Lcp

Background: Biodegradation of rubber (polyisoprene) is initiated by oxidative cleavage of the polyisoprene backbone and is performed either by an extracellular rubber oxygenase (RoxA) from Gram-negative rubber degrading bacteria or by a latex clearing protein (Lcp) secreted by Gram-positive rubber degrading bacteria. Only little is known on the biochemistry of polyisoprene cleavage by Lcp and on the types and functions of the involved cofactors. Results: A rubber-degrading bacterium was isolated from the effluent of a rubber-processing factory and was taxonomically identified as a Rhodococcus rhodochrous species. A gene of R. rhodochrous RPK1 that coded for a polyisoprene-cleaving latex clearing protein (lcp(Rr)) was identified, cloned, expressed in Escherichia coli and purified. Purified Lcp(Rr) had a specific activity of 3.1 U/mg at 30 degrees C and degraded poly(1,4-cis-isoprene) to a mixture of oligoisoprene molecules with terminal keto and aldehyde groups. The pH optimum of Lcp(Rr) was higher (pH 8) than for other rubber-cleaving enzymes (approximate to pH 7). UVvis spectroscopic analysis of Lcp(Rr) revealed a cytochrome-specific absorption spectrum with an additional feature at long wavelengths that has not been observed for any other rubber-cleaving enzyme. The presence of one b-type haem in Lcp(Rr) as a co-factor was confirmed by (i) metal analysis, (ii) solvent extraction, (iii) bipyridyl assay and (iv) detection of haem-b specific m/z values via mass-spectrometry. Conclusions: Our data point to substantial differences in the active sites of Lcp proteins obtained from different rubber degrading bacteria.