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Rubber oxygenase and latex clearing protein cleave rubber to different products and use different cleavage mechanisms.

ABSTRACT: Two types of enzyme for oxidative cleavage of poly(cis-1,4-isoprene) are known. One is rubber oxygenase (RoxA) that is secreted by Xanthomonas sp. strain 35Y and a few other Gram-negative rubber-degrading bacteria during growth on polyisoprene. RoxA was studied in the past, and the recently solved structure showed a structural relationship to bacterial cytochrome c peroxidases (J. Seidel et al., Proc. Natl. Acad. Sci. U. S. A. 110:13833-13838, 2013, http://dx.doi.org/10.1073/pnas.1305560110). The other enzyme is latex-clearing protein (Lcp) that is secreted by rubber-degrading actinomycetes, but Lcp has not yet been purified. Here, we expressed Lcp of Streptomyces sp. strain K30 in a ?roxA background of Xanthomonas sp. strain 35Y and purified native (untagged) Lcp. The specific activities of Lcp and RoxA were 0.70 and 0.48 U/mg, respectively. Lcp differed from RoxA in the absence of heme groups and other characteristics. Notably, Lcp degraded polyisoprene via endo-type cleavage to tetra-C20 and higher oligo-isoprenoids with aldehyde and keto end groups, whereas RoxA used an exo-type cleavage mechanism to give the main end product 12-oxo-4,8-dimethyltrideca-4,8-diene-1-al (ODTD). RoxA was able to cleave isolated Lcp-derived oligo-isoprenoid molecules to ODTD. Inhibitor studies, spectroscopic investigations and metal analysis gave no indication for the presence of iron, other metals, or cofactors in Lcp. Our results suggest that Lcp could be a member of the growing group of cofactor-independent oxygenases and differs in the cleavage mechanism from heme-dependent RoxA. In conclusion, RoxA and Lcp represent two different answers to the same biochemical problem, the cleavage of polyisoprene, a polymer that has carbon-carbon double bonds as the only functional groups for enzymatic attack.

SUBMITTER: Birke J

PROVIDER: S-EPMC4135767 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Rubber oxygenase and latex clearing protein cleave rubber to different products and use different cleavage mechanisms.

Birke Jakob J Jendrossek Dieter D

Applied and environmental microbiology 20140606 16

Two types of enzyme for oxidative cleavage of poly(cis-1,4-isoprene) are known. One is rubber oxygenase (RoxA) that is secreted by Xanthomonas sp. strain 35Y and a few other Gram-negative rubber-degrading bacteria during growth on polyisoprene. RoxA was studied in the past, and the recently solved structure showed a structural relationship to bacterial cytochrome c peroxidases (J. Seidel et al., Proc. Natl. Acad. Sci. U. S. A. 110:13833-13838, 2013, http://dx.doi.org/10.1073/pnas.1305560110). Th ...[more]

PMID: 24907333

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Project description:Only two types of rubber oxygenases, rubber oxygenase (RoxA) and latex clearing protein (Lcp), have been described so far. RoxA proteins (RoxAs) are c-type cytochromes of ?70 kDa produced by Gram-negative rubber-degrading bacteria, and they cleave polyisoprene into 12-oxo-4,8-dimethyltrideca-4,8-diene-1-al (ODTD), a C15 oligo-isoprenoid, as the major end product. Lcps are common among Gram-positive rubber degraders and do not share amino acid sequence similarities with RoxAs. Furthermore, Lcps have much smaller molecular masses (?40 kDa), are b-type cytochromes, and cleave polyisoprene to a mixture of C20, C25, C30, and higher oligo-isoprenoids as end products. In this article, we purified a new type of rubber oxygenase, RoxB Xsp (RoxB of Xanthomonas sp. strain 35Y). RoxB Xsp is distantly related to RoxAs and resembles RoxAs with respect to molecular mass (70.3 kDa for mature protein) and cofactor content (2 c-type hemes). However, RoxB Xsp differs from all currently known RoxAs in having a distinctive product spectrum of C20, C25, C30, and higher oligo-isoprenoids that has been observed only for Lcps so far. Purified RoxB Xsp revealed the highest specific activity of 4.5 U/mg (at 23°C) of all currently known rubber oxygenases and exerts a synergistic effect on the efficiency of polyisoprene cleavage by RoxA Xsp RoxB homologs were identified in several other Gram-negative rubber-degrading species, pointing to a prominent function of RoxB for the biodegradation of rubber in Gram-negative bacteria.IMPORTANCE The enzymatic cleavage of rubber (polyisoprene) is of high environmental importance given that enormous amounts of rubber waste materials are permanently released (e.g., by abrasion of tires). Research from the last decade has discovered rubber oxygenase A, RoxA, and latex clearing protein (Lcp) as being responsible for the primary enzymatic attack on the hydrophobic and water-insoluble biopolymer poly(cis-1,4-isoprene) in Gram-negative and Gram-positive rubber-degrading bacteria, respectively. Here, we provide evidence that a third type of rubber oxygenase is present in Gram-negative rubber-degrading species. Due to its characteristics, we suggest the designation RoxB for the new type of rubber oxygenase. Bioinformatic analysis of genome sequences indicates the presence of roxB homologs in other Gram-negative rubber degraders.

Project description:Gram-positive rubber degraders such as Streptomyces sp. strain K30 cleave rubber [poly(cis-1,4-isoprene)] to low-molecular-mass oligoisoprenoid products with terminal keto and aldehyde groups by the secretion of a latex clearing protein (Lcp) designated rubber oxygenase. LcpK30 is a heme b cytochrome and has a domain of unknown function (DUF2236) that is characteristic of orthologous Lcps. Proteins with a DUF2236 domain are characterized by three highly conserved residues (R164, T168, and H198 in LcpK30). Exchange of R164 or T168 by alanine and characterization of the purified LcpK30 muteins revealed that both were stable and contained a heme group (red color) but were inactive. This finding identifies both residues as key residues for the cleavage reaction. The purified H198A mutein was also inactive and stable but was colorless due to the absence of heme. We constructed and characterized alanine muteins of four additional histidine residues moderately conserved in 495 LcpK30 homologous sequences (H203A, H232A, H259A, H266A). All muteins revealed wild-type properties, excluding any importance for activity and/or heme coordination. Since LcpK30 has only eight histidines and the three remaining residues (H103, H184, and H296) were not conserved (<11%), H198 presumably is the only essential histidine, indicating its putative function as a heme ligand. The second axial position of the heme is likely occupied by a not yet identified molecule. Mutational analysis of three strictly conserved arginine residues (R195, R202, R328) showed that R195A and R202A muteins were colorless and instable, suggesting that these residues are important for the protein stability.ImportanceLarge amounts of rubber waste materials have been permanently released into the environment for more than a century, yet accumulation of rubber particles released, e.g., by abrasion of tires along highways has not been observed. This is indicative of the ubiquitous presence and activity of rubber-degrading microorganisms. Despite increasing research activities on rubber biodegradation during the last 2 decades, the knowledge of the enzymatic cleavage mechanism of rubber by latex clearing protein (Lcp) still is limited. In particular, the catalytic cleavage mechanism and the amino acids of Lcp proteins (Lcps) that are involved have not yet been identified for any Lcp. In this study, we investigated the importance of 10 amino acid residues of Lcp from Streptomyces sp. K30 (LcpK30) by mutagenesis, mutein purification, and biochemical characterization. We identified several essential residues, one of which most likely represents an axial heme ligand in Lcp of Streptomyces sp. K30.

Project description:About 22,000 1-methyl-3-nitro-1-nitrosoguanidine- and UV-induced mutants of the rubber-degrading bacterium Streptomyces sp. strain K30 were characterized for the ability to produce clear zones on natural rubber latex overlay agar plates. Thirty-five mutants were defective solely in cleavage of rubber and were phenotypically complemented with the wild-type lcp (latex clearing protein) gene. Sixty-nine mutants exhibited a pleiotropic phenotype and were impaired in utilization of rubber and xylan, indicating that the enzymes responsible for the initial cleavage of these polymers are exported by the same secretion pathway (Q. K. Beg, M. Kapoor, L. Mahajan, and G. S. Hoondal, Appl. Microbiol. Biotechnol. 56:326-3381, 2001; U. K. Laemmli, Nature 227:680-685, 1970). Analysis of the amino acid sequence encoded by lcp revealed a twin-arginine motif, indicating that Lcp is a substrate of the twin-arginine translocation (Tat) pathway (K. Dilks, W. Rose, E. Hartmann, and M. Pohlschröder, J. Bacteriol. 185:1478-1483, 2003). A tatC disruption mutant of Streptomyces lividans 10-164 harboring lcp from Streptomyces sp. strain K30 was not capable of forming clear zones on rubber overlay agar plates. Moreover, Lcp and enhanced green fluorescent protein fusion proteins were detected in the supernatant. Using Escherichia coli having the twin-arginine motif in the signal peptide upstream of Lcp, clear evidence that Lcp is secreted was obtained. Transcriptional analysis revealed basal expression of Lcp in glucose-grown cells and that transcription of lcp is obviously induced in the presence of poly(cis-1,4-isoprene). In contrast, oxiB and oxiA, which are located directly downstream of lcp and putatively encode a heteromultimeric aldehyde dehydrogenase oxidizing the primary cleavage products generated by Lcp from poly(cis-1,4-isoprene), were expressed only in the presence of poly(cis-1,4-isoprene). Expression of lcp at a low level is thus required for sensing the polymer in the medium. Rubber degradation products may then induce the transcription of genes coding for enzymes catalyzing the later steps of poly(cis-1,4-isoprene) degradation and the transcription of lcp itself. lcp, oxiB, and oxiA seem to constitute an operon, as a polycistronic mRNA comprising these three genes was detected. The transcriptional start site of lcp was mapped 400 bp upstream of the lcp start codon.

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Rubber oxygenase and latex clearing protein cleave rubber to different products and use different cleavage mechanisms.

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Rubber oxygenase and latex clearing protein cleave rubber to different products and use different cleavage mechanisms.

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