Structure of the hypothetical<i>Mycoplasma</i>protein MPN555 suggests a chaperone function

Schulze‐Gahmen, Ursula; Aono, Shelly; Yokota, Hisao; Kim, Rosalind; Kim, Sung Hou

doi:10.1107/s090744490502264x

Cited by 13 publications

(12 citation statements)

References 12 publications

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“…The C terminus of TF is a putative chaperone module. TF, SurA, and MPN555 share the same structural features (11,35,36) in their putative chaperone active domain, composed of a single helix (green), a two-helix arm (red), and a three-helix arm (blue).…”

Section: Discussionmentioning

confidence: 99%

The C-terminal Domain ofEscherichia coliTrigger Factor Represents the Central Module of Its Chaperone Activity

Merz¹,

Hoffmann²,

Rutkowska³

et al. 2006

J. Biol. Chem.

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In bacteria, ribosome-bound Trigger Factor assists the folding of newly synthesized proteins. The N-terminal domain (N) of Trigger Factor mediates ribosome binding, whereas the middle domain (P) harbors peptidyl-prolyl isomerase activity. The function of the C-terminal domain (C) has remained enigmatic due to structural instability in isolation. Here, we have characterized a stabilized version of the C domain (C S ), designed on the basis of the recently solved atomic structure of Trigger Factor. Strikingly, only the isolated C S domain or domain combinations thereof (NC S , PC S ) revealed substantial chaperone activity in vitro and in vivo. Furthermore, to disrupt the C domain without affecting the overall Trigger Factor structure, we generated a mutant (⌬53) by deletion of the C-terminal 53 amino acid residues. This truncation caused the complete loss of the chaperone activity of Trigger Factor in vitro and severely impaired its function in vivo. Therefore, we conclude that the chaperone activity of Trigger Factor critically depends on its C-terminal domain as the central structural chaperone module. Intriguingly, a structurally similar module is found in the periplasmic chaperone SurA and in MPN555, a protein of unknown function. We speculate that this conserved module can exist solely or in combination with additional domains to fulfill diverse chaperone functions in the cell.

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Section: Discussionmentioning

confidence: 99%

The C-terminal Domain ofEscherichia coliTrigger Factor Represents the Central Module of Its Chaperone Activity

Merz¹,

Hoffmann²,

Rutkowska³

et al. 2006

J. Biol. Chem.

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“…Moreover, the PPIase domain binds preferentially to peptide segments of at least eight amino acids that are enriched in basic and aromatic amino acids but do not necessarily contain proline residues, suggesting a more general chaperone function (18,19). The C-domain shows structural similarity to the periplasmic chaperone SurA (20) and to MPN555 of Mycoplasma pneumoniae, a predicted protein of unknown function (21). This domain can be divided into two subdomains consisting of arm 1 and arm 2.…”

mentioning

confidence: 99%

Identification of Nascent Chain Interaction Sites on Trigger Factor

Lakshmipathy

Tomic

Kaiser

et al. 2007

Journal of Biological Chemistry

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The role of ribosome-binding molecular chaperones in protein folding is not yet well understood. Trigger factor (TF) is the first chaperone to interact with nascent polypeptides as they emerge from the bacterial ribosome. It binds to the ribosome as a monomer but forms dimers in free solution. Based on recent crystal structures, TF has an elongated shape, with the peptidylprolyl-cis/trans-isomerase (PPIase) domain and the N-terminal ribosome binding domain positioned at opposite ends of the molecule and the C-terminal domain, which forms two arms, positioned in between. By using site specifically labeled TF proteins, we have demonstrated that all three domains of TF interact with nascent chains during translation. Interactions with the PPIase domain were length-dependent but independent of PPIase activity. Interestingly, with free TF, these same sites were found to be involved in forming the dimer interface, suggesting that dimerization partially occludes TF-nascent chain binding sites. Our data indicate the existence of two regions on TF along which nascent chains can interact, the NC-domains as the main site and the PPIase domain as an auxiliary site.

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“…The C-terminal domain of TF consists of a crevice surrounded by two arm-like structures (18) similar to the N-terminal domain of the E. coli periplasmic chaperone SurA and Mycoplasma pneumoniae MPN555 (21)(22)(23). Based on photocross-linking, both arms were found to be adjacent to the nascent chain during translation (17,24).…”

mentioning

confidence: 99%

Versatility of Trigger Factor Interactions with Ribosome-Nascent Chain Complexes

Lakshmipathy

Gupta²,

Pinkert

et al. 2010

Journal of Biological Chemistry

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Trigger factor (TF) is the first molecular chaperone that interacts with nascent chains emerging from bacterial ribosomes. TF is a modular protein, consisting of an N-terminal ribosome binding domain, a PPIase domain, and a C-terminal domain, all of which participate in polypeptide binding. To directly monitor the interactions of TF with nascent polypeptide chains, TF variants were site-specifically labeled with an environmentally sensitive NBD fluorophore. We found a marked increase in TF-NBD fluorescence during translation of firefly luciferase (Luc) chains, which expose substantial regions of hydrophobicity, but not with nascent chains lacking extensive hydrophobic segments. TF remained associated with Luc nascent chains for 111 ؎ 7 s, much longer than it remained bound to the ribosomes (t1 ⁄ 2 ϳ 10 -14 s). Thus, multiple TF molecules can bind per nascent chain during translation. The Escherichia coli cytosolic proteome was classified into predicted weak and strong interactors for TF, based on the occurrence of continuous hydrophobic segments in the primary sequence. The residence time of TF on the nascent chain generally correlated with the presence of hydrophobic regions and the capacity of nascent chains to bury hydrophobicity. Interestingly, TF bound the signal sequence of a secretory protein, pOmpA, but not the hydrophobic signal anchor sequence of the inner membrane protein FtsQ. On the other hand, proteins lacking linear hydrophobic segments also recruited TF, suggesting that TF can recognize hydrophobic surface features discontinuous in sequence. Moreover, TF retained significant affinity for the folded domain of the positively charged, ribosomal protein S7, indicative of an alternative mode of TF action. Thus, unlike other chaperones, TF appears to employ multiple mechanisms to interact with a wide range of substrate proteins.

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Structure of the hypotheticalMycoplasmaprotein MPN555 suggests a chaperone function

Cited by 13 publications

References 12 publications

The C-terminal Domain ofEscherichia coliTrigger Factor Represents the Central Module of Its Chaperone Activity

The C-terminal Domain ofEscherichia coliTrigger Factor Represents the Central Module of Its Chaperone Activity

Identification of Nascent Chain Interaction Sites on Trigger Factor

Versatility of Trigger Factor Interactions with Ribosome-Nascent Chain Complexes

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