The mannitol-specific enzyme II (mtlA) gene and the mtlR gene of the PTS of Streptococcus mutans The GenBank accession number for the sequence reported in this paper is AF210133.

Abstract

The phosphoenolpyruvate-dependent phosphotransferase system (PTS) is widely found among Gram-positive bacteria. It is the major source of carbohydrate transport in the dental pathogen Streptococcus mutans. The transported carbohydrates are fermented to produce large amounts of lactic acid which initiates dental caries. The authors have isolated the S. mutans gene for the mannitol-specific Enzyme II (EII) component of the PTS, mtlA, and the adjacent mtlR gene, which is located in the same operon. The mtlR gene is located between mtlA and the genes mtlF and mtlD. The nucleotide sequence of the mtlA and mtlR loci has been determined. The deduced mtlA gene product of S. mutans consists of 589 amino acids with a molecular mass of 620 kDa. It exhibits similarity with the mtlA gene products from other organisms. However, the similarity between these proteins is generally restricted to the 470 amino-terminal residues of the S. mutans protein. This region would correspond to the EIICB domains of the PTS. The authors have previously shown that the S. mutans mtlF gene product exhibits 766% similarity to the carboxyl-terminal 143 amino acids of the Escherichia coli mtlA product and that the mtlF gene encodes the EIIA domain of the PTS. Thus, the genes that encode the EIICB and the EIIA domains are separated by approximately 2250 bp. In many organisms, all of the EII domains may be fused together to form one molecule. The fact that these domains are separated by this distance in S. mutans supports the hypothesis that various functional domains of the PTS have been rearranged during evolution. The sequence of the 119 carboxyl-terminal amino acids of the S. mutans mtlA gene product also displays homology to the carboxyl-terminal end of the EIIB domain of various mannitol PTSs. Thus, this domain may have been duplicated in S. mutans during evolution of the operon. The mtlR gene is located in the same operon structure as mtlA but these loci are separated by an intragenic space. The precise 5' end of the mtlR locus cannot be determined either by in vitro transcription-translation assays or based upon nucleotide sequence analysis because of the apparent lack of a ribosome-binding site preceding the gene. The deduced mtlR gene product, which consists of approximately 650 amino acids with a molecular mass of 753 kDa, exhibits limited similarity to several potential transcriptional regulators. However, the exact function of this locus is currently unknown.

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

“…In addition, the mtl operon of S. aureus exhibits a gene order (mtlARFD) identical to those in G. stearothermophilus and S. mutans (341,342). In contrast, ydaA, which encodes the B. subtilis MtlR homolog, is a monocistronic transcription unit located about 15 kb downstream from the mtl operon (437).…”

“…MtlR of S. mutans exhibits only 28% sequence identity and 48% similarity to MtlR of G. stearothermophilus. Surprisingly, only a polar insertion into mtlR was reported to prevent mannitol utilization by S. mutans, whereas a nonpolar insertion had no effect (342). Therefore, (51).…”

Molecular analysis of the mannitol operon of Clostridium acetobutylicum encoding a phosphotransferase system and a putative PTS-modulated regulator

“…By demonstrating the existence of a mannitolspecific PTS component in both soluble and membrane fractions of cell extracts, our data obtained in phosphorylation studies confirm a separation of mannitol enzyme II into membrane-bound EIICB Mtl and cytoplasmic IIA Mtl components. The corresponding genes mtlA and mtlF are separated by the mtlR gene encoding the putative multi-domain regulator of the mannitol PTS, again emphasizing that mannitol loci in several Gram-positive bacteria exhibit similar characteristics and gene arrangements (Henstra et al, 1999 ;Honeyman & Curtiss, 2000). 6.…”

“…MtlR of C. acetobutylicum exhibits greatest identity (25n4 %) to the MtlR protein of B. stearothermophilus (Henstra et al, 1999). Similar transcriptional regulators are encoded within the lic (lichenan) operon of B. subtilis (LicR ; Tobisch et al, 1997), by the ydaA gene of B. subtilis, for which the name mtlR has recently been proposed (Stu$ lke et al, 1998), and by the mtlR and srlR genes of the Streptococcus mutans mannitol and sorbitol operons respectively (Honeyman & Curtiss, 2000 ;Boyd et al, 2000). The central part of MtlR comprises two PTS regulatory domains (PRDs), which are found in each of these proteins, as well as in the B. subtilis transcriptional regulator LevR and in transcriptional antiterminator proteins of the BglG family (Tortosa et al, 1997 ;Stu$ lke et al, 1998).…”

“…The His phosphorylation site is marked by an asterisk. MtlR (Smu), MtlR of Streptococcus mutans (AF210133, Honeyman & Curtiss, 2000) ; PtsN (Eco), IIA Ntr of Escherichia coli (P31222, Powell et al, 1995) ; PtsN (Kpn), IIA Ntr of Klebsiella pneumoniae (P17162, Merrick & Coppard, 1989) ; SrlR (Smu), SrlR of Streptococcus mutans (AF132127, Boyd et al, 2000) ; other abbreviations as for (a). The residue number of the amino acid at each end of the alignment is shown.…”