Structure and evolution of a multidomain multiphosphoryl transfer protein. Nucleotide sequence of the fruB(HI) gene in Rhodobacter capsulatus and comparisons with homologous genes from other organisms

Abstract

The gene order of the fructose (fru) operon and nucleotide sequence of the first gene (fruB(HI) of Rhodobacter capsulatus are reported, analyzed and compared with homologous genes from other bacteria, and the gene products are identified. Included within the region reported is a gene encoding a multiphosphoryl transfer protein (MTP) of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). MTP consists of three moieties: a fructose-specific enzyme III (IIIfru)-like N-terminal moiety (residues 1 to 143) followed by an FPr(HPr)-like moiety (residues 157 to 245) and an enzyme I-like moiety (residues 273 to 827). The enzyme III-like moiety closely resembles the N-terminal 143 residues of the IIIfru-FPR fusion protein from Salmonella typhimurium (40.6% identity throughout its length) and the C-terminal 145 residues of the mannitol-specific enzyme II (IImtl) (37.8% identity throughout its length with the IIImtl moiety of IImtl). The FPr-like domain of MTP resembles the S. typhimurium FPr (42.4% identity) and the Escherichia coli or S. typhimurium HPr (38.8% identity). The enzyme I-like moiety resembles the E. coli enzyme I (38.9% identity). Predicted phosphorylation sites within the three functional units of MTP (His62 in the IIIfru-like moiety; His171 in the FPr-like moiety and His457 in the enzyme I-like moiety) were identified on the basis of sequence comparisons with the homologous proteins from enteric bacteria. The three functional domains of MTP are joined by two flexible "linkage" regions, rich in alanine, glycine and proline, which show 47% sequence identity with each other. They also exhibit a high degree of sequence identity with the linkage region of the mannose-specific enzyme III (IIIman) of the E. coli PTS as well as several other proteins of bacterial, eukaryotic and viral origin. At the RNA level, these linker regions formed hairpin structures with high (90%) G + C content. Analyses of the IIIfru-FPr fusion protein of S. typhimurium revealed that between the IIIfru and FPr moieties of this protein is a stretch of 142 amino acids that do not show homology to known PTS proteins. This region and the adjacent FPr-like region contain a sequence of 110 residues exhibiting 59% similarity to the receiver consensus motif defined by Kofoid and Parkinson. Because the Salmonella IIIfru-FPr fusion protein has been implicated in transcriptional regulation, this region of the Salmonella protein may prove to have regulatory significance.(ABSTRACT TRUNCATED AT 400 WORDS)