Large Is Fast, Small Is Tight: Determinants of Speed and Affinity in Subunit Capture by a Periplasmic Chaperone

Yu, Xiao Di; Fooks, L.J.; Moslehi-Mohebi, E.; Tischenko, V. M.; Askarieh, Gelareh; Knight, Stefan D.; MacIntyre, Sheila; Zavialov, Anton V.

doi:10.1016/j.jmb.2012.01.020

Cited by 23 publications

(36 citation statements)

References 29 publications

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“…It is remarkable that Class 5 chaperones also share two features in common with FGS chaperones (Table 2). First, like FGS chaperones the Class 5 chaperones lack an N-terminal extension preceding the N-terminal A1 strand that is essential for subunit binding by FGL chaperones [28] (Fig. 3).…”

Section: Resultsmentioning

confidence: 99%

Structure of CfaA Suggests a New Family of Chaperones Essential for Assembly of Class 5 Fimbriae

et al. 2014

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Adhesive pili on the surface of pathogenic bacteria comprise polymerized pilin subunits and are essential for initiation of infections. Pili assembled by the chaperone-usher pathway (CUP) require periplasmic chaperones that assist subunit folding, maintain their stability, and escort them to the site of bioassembly. Until now, CUP chaperones have been classified into two families, FGS and FGL, based on the short and long length of the subunit-interacting loops between its F1 and G1 β-strands, respectively. CfaA is the chaperone for assembly of colonization factor antigen I (CFA/I) pili of enterotoxigenic E. coli (ETEC), a cause of diarrhea in travelers and young children. Here, the crystal structure of CfaA along with sequence analyses reveals some unique structural and functional features, leading us to propose a separate family for CfaA and closely related chaperones. Phenotypic changes resulting from mutations in regions unique to this chaperone family provide insight into their function, consistent with involvement of these regions in interactions with cognate subunits and usher proteins during pilus assembly.

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Section: Resultsmentioning

confidence: 99%

Structure of CfaA Suggests a New Family of Chaperones Essential for Assembly of Class 5 Fimbriae

et al. 2014

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“…Therefore, substitution of alanine for I33 resulted in loss of the CssA-CssB complex because of a loss of hydrophobic interactions. It is also known that P5 is the site of DSE initiation and must be occupied by a large donor residue such as Ile (21,22). Therefore, in the case of the CssA I33A mutant protein, DSE is perturbed, which leads to subsequent disruption of CS6 assembly.…”

Section: Discussionmentioning

confidence: 99%

Functional Role of N- and C-Terminal Amino Acids in the Structural Subunits of Colonization Factor CS6 Expressed by Enterotoxigenic Escherichia coli

et al. 2016

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CS6 is a common colonization factor expressed by enterotoxigenic Escherichia coli. It is a two-subunit protein consisting of CssA and CssB in an equal stoichiometry, assembled via the chaperone-usher pathway into an afimbrial, oligomeric assembly on the bacterial cell surface. A recent structural study has predicted the involvement of the N-and C-terminal regions of the CS6 subunits in its assembly. Here, we identified the functionally important residues in the N-and C-terminal regions of the CssA and CssB subunits during CS6 assembly by alanine scanning mutagenesis. Bacteria expressing mutant proteins were tested for binding with Caco-2 cells, and the results were analyzed with respect to the surface expression of mutant CS6. In this assay, many mutant proteins were not expressed on the surface while some showed reduced expression. It appeared that some, but not all, of the residues in both the N and C termini of CssA and CssB played an important role in the intermolecular interactions between these two structural subunits, as well as chaperone protein CssC. Our results demonstrated that T20, K25, F27, S36, Y143, and V147 were important for the stability of CssA, probably through interaction of CssC. We also found that I22, V29, and I33 of CssA and G154, Y156, L160, V162, F164, and Y165 of CssB were responsible for CssA-CssB intermolecular interactions. In addition, some of the hydrophobic residues in the C terminus of CssA and the N terminus of CssB were involved in the stabilization of higher-order complex formation. Overall, the results presented here might help in understanding the pathway used to assemble CS6 and predict its structure. IMPORTANCEUnlike most other colonization factors, CS6 is nonfimbrial, and in a sense, its subunit composition and assembly are also unique. Here we report that both the N-and C-terminal amino acid residues of CssA and CssB play a critical role in the intermolecular interactions between them and assembly proteins. We found mainly that alternate hydrophobic residues present in these motifs are essential for the interaction between the structural subunits, as well as the chaperone and usher assembly proteins. Our results indicate the involvement of the side chains of identified amino acids in CS6 assembly. This study adds a step toward understanding the interactions between structural subunits of CS6 and assembly proteins during CS6 biogenesis. Enterotoxigenic Escherichia coli (ETEC) infection is the most common cause of infantile diarrhea, which accounts for approximately 210 million episodes and 380,000 deaths annually (1). Plasmid-encoded colonization factors (CFs) and heat-labile and heat-stable (LT and ST, respectively) enterotoxins are the major determinants of ETEC virulence. Colonization is the prerequisite step in initiating the virulence mediated by the interaction of CFs with their cognate receptors on the intestinal epithelium. So far, 25 different CFs have been identified and subdivided on the basis of antigenicity, molecular weight, and structural morpholo...

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“…The G1 β-strand donated by the chaperone contains a conserved motif of alternating hydrophobic residues, and during donor strand exchange these residues insert into the P1–4 pockets of the subunit, forming a β-zipper interaction (55,86). In FGL chaperones, the longer G1 donor strand fills the P5 binding pocket as well, but this interaction is weaker than at the other pockets (86,87). The chaperone G1 β-strand is inserted parallel to the F strand of the subunit, forming a non-canonical Ig fold.…”

Section: Adhesins Expressed By Gram-negative Uropathogensmentioning

confidence: 99%

“…The chaperone G1 β-strand is inserted parallel to the F strand of the subunit, forming a non-canonical Ig fold. This, together with the large size of the residues inserted by the chaperone maintains pilins in an open, “activated” state, which enables subsequent assembly into the pilus fiber (54,55,87). The groove of the pilin domain is also the site of subunit-subunit interactions, which are mediated by the donor strand exchange reaction as described above for the pilus fiber (54,55).…”

Section: Adhesins Expressed By Gram-negative Uropathogensmentioning

confidence: 99%

“…At the usher, the hydrophobic residues of the Nte from an incoming chaperone-subunit complex insert into the subunit groove of the preceding chaperone-subunit complex bound at the usher, displacing the donated G1 β-strand of the chaperone from the preceding subunit by a concerted strand displacement mechanism that initiates at the P5 pocket (54,55,86,94,95). In contrast to the donated chaperone β-strand, the Nte is inserted anti-parallel to the F strand of the preceding subunit and inserts smaller-sized residues into the subunit groove, thus completing the Ig fold of the pilin domain in a canonical fashion and allowing the subunit to adopt a highly stable final state (54,55,60,87). ATP is not available in the periplasm and pilus biogenesis at the outer membrane usher does not require input from other energy sources (96,97).…”

Section: Adhesins Expressed By Gram-negative Uropathogensmentioning

confidence: 99%

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Structure, Function, and Assembly of Adhesive Organelles by Uropathogenic Bacteria

Chahales

Thanassi

2015

Microbiol Spectr

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Bacteria assemble a wide range of adhesive proteins, termed adhesins, to mediate binding to receptors and colonization of surfaces. For pathogenic bacteria, adhesins are critical for early stages of infection, allowing the bacteria to initiate contact with host cells, colonize different tissues, and establish a foothold within the host. The adhesins expressed by a pathogen are also critical for bacterial-bacterial interactions and the formation of bacterial communities such as biofilms. The ability to adhere to host tissues is particularly important for bacteria that colonize sites such as the urinary tract, where the flow of urine functions to maintain sterility by washing away non-adherent pathogens. Adhesins vary from monomeric proteins that are directly anchored to the bacterial surface to polymeric, hairlike fibers that extend out from the cell surface. These latter fibers are termed pili or fimbriae, and were among the first identified virulence factors of uropathogenic Escherichia coli. Studies since then have identified a range of both pilus and non-pilus adhesins that contribute to bacterial colonization of the urinary tract, and have revealed molecular details of the structures, assembly pathways, and functions of these adhesive organelles. In this review, we describe the different types of adhesins expressed by both Gram-negative and Gram-positive uropathogens, what is known about their structures, how they are assembled on the bacterial surface, and the functions of specific adhesins in the pathogenesis of urinary tract infections.

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Large Is Fast, Small Is Tight: Determinants of Speed and Affinity in Subunit Capture by a Periplasmic Chaperone

Cited by 23 publications

References 29 publications

Structure of CfaA Suggests a New Family of Chaperones Essential for Assembly of Class 5 Fimbriae

Structure of CfaA Suggests a New Family of Chaperones Essential for Assembly of Class 5 Fimbriae

Functional Role of N- and C-Terminal Amino Acids in the Structural Subunits of Colonization Factor CS6 Expressed by Enterotoxigenic Escherichia coli

Structure, Function, and Assembly of Adhesive Organelles by Uropathogenic Bacteria

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