RESUMO
The Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system (PTS) in prokaryotes mediates the uptake and phosphorylation of its numerous substrates through a phosphoryl transfer chain where a phosphoryl transfer protein, HPr, transfers its phosphoryl group to any of several sugar-specific Enzyme IIA proteins in preparation for sugar transport. A phosphoryl transfer protein of the PTS, NPr, homologous to HPr, functions to regulate nitrogen metabolism and shows virtually no enzymatic cross-reactivity with HPr. Here we describe the genetic engineering of a "chimeric" HPr/NPr protein, termed CPr14 because 14 amino acid residues of the interface were replaced. CPr14 shows decreased activity with most PTS permeases relative to HPr, but increases activity with the broad specificity mannose permease. The results lead to the proposal that HPr is not optimal for most PTS permeases but instead represents a compromise with suboptimal activity for most PTS permeases. The evolutionary implications are discussed.
Assuntos
Proteínas de Bactérias/metabolismo , Proteínas de Transporte/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Engenharia Genética , Sistema Fosfotransferase de Açúcar do Fosfoenolpiruvato/metabolismo , Proteínas Recombinantes de Fusão/metabolismo , Proteínas de Bactérias/genética , Proteínas de Transporte/genética , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Proteínas de Ligação a Fosfato , Sistema Fosfotransferase de Açúcar do Fosfoenolpiruvato/genética , Proteínas Recombinantes de Fusão/genética , Especificidade por Substrato/genéticaRESUMO
The TqsA (YdgG) protein of Escherichia coli has been shown to export the autoinducer-2 (AI-2) molecule, a furanosyl borate diester that bears little resemblance to previously characterized biological molecules. TqsA belongs to a large superfamily, the AI-2 exporter (AI-2E) superfamily, of putative transporters with no other functionally characterized members. These proteins derive exclusively from bacteria. Many different bacterial kingdoms contain them, although several kingdoms do not. These proteins exhibit a uniform topology with 8 putative transmembrane segments (TMSs) which we show probably arose from a 4-TMS precursor in a process that involved at least one and possibly two intragenic duplication event(s). The first halves of these proteins are more diverse in sequence than the second halves, suggesting that the first halves may serve substrate-specific functions while the second halves serve family-specific functions. Conserved residues and motifs in these proteins are identified. Some homologues include extra catalytic domains including those involved in purine nucleotide biosynthesis, ATP and GTP binding, and molecular signaling. The results presented provide guides for future functional studies on members of this superfamily of bacterial transporters.