RESUMO
Among the large number of hypothetical proteins within the genomes of Helicobacter pylori, there is a family of unique and highly disulfide-bridged proteins, designated family 12, for which no function could originally be assigned. Sequence analysis revealed that members of this family possess a modular architecture of alpha/beta-units and a stringent pattern of cysteine residues. The H. pylori cysteine-rich protein A (HcpA), which is a member of this family, was expressed and refolded from inclusion bodies. Six pairs of cysteine residues, which are separated by exactly seven residues, form disulfide bridges. HcpA is a beta-lactamase. It slowly hydrolyzes 6-aminopenicillinic acid and 7-aminocephalosporanic acid (ACA) derivatives. The turnover for 6-aminopenicillinic acid derivatives is 2-3 times greater than for ACA derivatives. The enzyme is efficiently inhibited by cloxacillin and oxacillin but not by ACA derivatives or metal chelators. We suggest that all family 12 members possess similar activities and might be involved in the synthesis of the cell wall peptidoglycan. They might also be responsible for amoxicillin resistance of certain H. pylori strains.
Assuntos
Cisteína , Helicobacter pylori/enzimologia , beta-Lactamases/química , beta-Lactamases/metabolismo , Sequência de Aminoácidos , Proteínas de Bactérias , Dissulfetos , Guanidina , Helicobacter pylori/genética , Cinética , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Desnaturação Proteica , Dobramento de Proteína , Sinais Direcionadores de Proteínas/química , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Especificidade por Substrato , beta-Lactamases/genéticaRESUMO
A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.
Assuntos
Bactérias/metabolismo , Água Doce/microbiologia , Sulfetos/metabolismo , Ecossistema , Oxirredução , Suíça , Microbiologia da ÁguaRESUMO
We describe a case of leiomyoma in the breast in a 48-year-old woman. The main clinical-pathologic features together with the differential diagnosis, and the pertinent literature reviewed.
