The Filamentous Phages fd and IF1 Use Different Mechanisms to Infect Escherichia coli
ABSTRACT The filamentous phage fd uses its gene 3 protein (G3P) to target Escherichia coli cells in a two-step process. First, the N2 domain of G3P attaches to an F pilus, and then the N1 domain binds to TolA-C. N1 and N2 are tightly associated, rendering the phage robust but noninfectious because the binding site for TolA-C is buried at the domain interface. Binding of N2 to the F pilus initiates partial unfolding, domain disassembly, and prolyl cis-to-trans isomerization in the hinge between N1 and N2. This activates the phage, and trans-Pro213 maintains this state long enough for N1 to reach TolA-C. Phage IF1 targets I pili, and its G3P contains also an N1 domain and an N2 domain. The pilus-binding N2 domains of the phages IF1 and fd are unrelated, and the N1 domains share a 31% sequence identity. We show that N2 of phage IF1 mediates binding to the I pilus, and that N1 targets TolA. Crystallographic and NMR analyses of the complex between N1 and TolA-C indicate that phage IF1 interacts with the same site on TolA-C as phage fd. In IF1-G3P, N1 and N2 are independently folding units, however, and the TolA binding site on N1 is permanently accessible. Activation by unfolding and prolyl isomerization, as in the case of phage fd, is not observed. In IF1-G3P, the absence of stabilizing domain interactions is compensated for by a strong increase in the stabilities of the individual domains. Apparently, these closely related filamentous phages evolved different mechanisms to reconcile robustness with high infectivity.
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- "Interestingly, the type IV pili are evolutionarily unrelated to the conjugative pili (including F and N) and completely different in the mode of their assembly and in morphology, hence the pIII-pilus interactions in phage that utilize them as primary receptors are likely very different from those of Ff. An approach using chimeric pIII molecules showed that the primary receptorbinding domain (N2) of pIII from phage IF1 and CTXφ allow f1 to infect the I-pilus containing E. coli and TCP piluscontaining V. cholerae, respectively (Heilpern and Waldor, 2003; Lorenz et al., 2011). The efficiency of infection, mediated by chimeric pIII proteins, however, decreases by several orders of magnitude if the distance between the three domains (N1, N2 and C) is changed by inserting additional domains (Heilpern and Waldor, 2003; Marzari et al., 1997). "
ABSTRACT: Filamentous bacteriophage, long and thin filaments that are secreted from the host cells without killing them, have been an antithesis to the standard view of head-and-tail bacterial killing machines. Episomally replicating filamentous phage Ff of Escherichia coli provide the majority of information about the principles and mechanisms of filamentous phage infection, episomal replication and assembly. Chromosomally- integrated "temperate" filamentous phage have complex replication and integration, which are currently under active investigation. The latter are directly or indirectly implicated in diseases caused by bacterial pathogens Vibrio cholerae, Pseudomonas aeruginosa and Neisseria meningitidis. In the first half of the review, both the Ff and temperate phage are described and compared. A large section of the review is devoted to an overview of phage display technology and its applications in nanotechnology.Current issues in molecular biology 04/2011; 13(2):51-76. DOI:10.1002/9780470015902.a0000777 · 5.75 Impact Factor
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- "In IF1-G3P, the TolA binding site is always accessible, because the N1 and N2 do not interact. The N1 domain of phage IF1 thus binds to TolA-C equally well as an isolated domain and as a part of G3P (Lorenz et al., 2011). The Db6 variant of fd-G3P* bound to TolA-C virtually with the same kinetics (Fig. 2E) and the same affinity (Fig. 2F) as its isolated N1 domain, indicating that the removal of strand b6 weakened the domain interactions in fd-G3P* so strongly that the TolA binding site is now fully accessible for TolA-C. "
ABSTRACT: When they infect Escherichia coli cells, the filamentous phages IF1 and fd first interact with a pilus and then target TolA as their common receptor. They use the domains N2 and N1 of their gene-3-proteins (G3P) for these interactions but differ in the mechanism of infection. In G3P of phage IF1, N1 and N2 are independent modules that are permanently binding-active. G3P of phage fd is usually in a closed state in which N1 and N2 are tightly associated. The TolA binding site is thus inaccessible and the phage incompetent for infection. Partial unfolding and prolyl isomerization must occur to abolish the domain interactions and expose the TolA binding site. This complex mechanism of phage fd could be changed to the simple infection mechanism of phage IF1 by reprogramming its G3P following physicochemical rules of protein stability. The redesigned phage fd was robust and as infectious as wild-type phage fd.Molecular Microbiology 03/2011; 80(3):827-34. DOI:10.1111/j.1365-2958.2011.07617.x · 4.42 Impact Factor
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ABSTRACT: Analysis of water and sand samples was done by reflectance measurements using a mobile phone. The phone's screen served as light source and front view camera as detector. Reflected intensities for white, red, green and blue colors were used to do principal component analysis for classification of several compounds and their concentrations in water. Analyses of colored solutions and colorimetric reactions based on widely available chemicals were performed. Classification of iron(III), chromium(VI) and sodium salt of humic acid was observed using reflected intensities from blue and green light for concentrations 2-10mg/l. Addition of complex forming sodium salt of ethylenediaminetetraacidic acid enabled the discrimination of Cu(II) ions in the 2-10mg/l concentration range based on reflection of red light. An alternate method using test strips for copper solutions with the phone as reader also demonstrated a detection limit of 2mg/l. Analysis of As(III) from 25 to 400 μg/l based on reflection of red light was performed utilizing the bleaching reaction of tincture of iodine containing starch. Enhanced sensitivity to low concentrations of arsenic was obtained by including reflected intensities from white light in the analysis. Model colored sand samples representing discoloration caused by the presence of arsenic in groundwater were analyzed as a complementary method for arsenic detection.Talanta 05/2011; 84(4):1118-23. DOI:10.1016/j.talanta.2011.03.016 · 3.55 Impact Factor