Sequence analysis of a gene product synthesized by Xanthomonas sp. during growth on natural rubber latex

Abstract

Xanthomonas sp. secretes an extracellular protein ( M r≈70±5 kDa) during growth on purified natural rubber [poly(1,4- cis-isoprene)] but not during growth on water-soluble carbon sources such as glucose or gluconate. A 1.3 kbp DNA fragment coding for an internal part of the structural gene of the 70 kDa protein was amplified by nested polymerase chain reaction (PCR) using amino acid sequence information obtained after Edman degradation of selected trypsin-generated peptides of the purified 70 kDa protein. The PCR product was used as a DNA probe to clone the complete structural gene from genomic DNA of Xanthomonas sp. The sequenced DNA contained a 2037 bp open reading frame which coded for a polypeptide of 678 amino acids ( M r 74.6 kDa) and which included the features of the N-terminal signal peptidase cleavage site ( M r≈72.9 kDa for the mature protein). Analysis of the amino acid sequence revealed the presence of two heme binding motifs (CXXCH) and a ≈20 amino acids long sequence that is conserved in the Paracoccus denitrificans and Pseudomonas aeruginosa diheme cytochrome c peroxidases (CCPs). This region includes a histidine residue (H 519 in Xanthomonas sp. and H 265 and H 271 in the Pseudomonas strains, respectively) that is essential for activity in CCPs and that is also conserved in other bacterial oxidases. Blast analysis confirmed the relatedness of the 70 kDa protein to heme-containing oxidases and suggested that it is a member of a new family of relatively large (≈500 to ≈1000 amino acids) extracellular proteins with so far unknown function being only far related in amino acid sequence to P. denitrificans and P. aeruginosa CCPs.