RoxB Is a Novel Type of Rubber Oxygenase That Combines Properties of Rubber Oxygenase RoxA and Latex Clearing Protein (Lcp)

摘要

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 approximate to 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 C-15 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 (approximate to 40 kDa), are b-type cytochromes, and cleave polyisoprene to a mixture of C-20, C-25, C-30, 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 degrees 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.