Cooperation of the Prolyl Isomerase and Chaperone Activities of the Protein Folding Catalyst SlyD
ABSTRACT The SlyD (sensitive to lysis D) protein of Escherichia coli is a folding enzyme with a chaperone domain and a prolyl isomerase domain of the FK506 binding protein type. Here we investigated how the two domains and their interplay are optimized for function in protein folding. Unfolded protein molecules initially form a highly dynamic complex with the chaperone domain of SlyD, and they are then transferred to the prolyl isomerase domain. The turnover number of the prolyl isomerase site is very high and guarantees that, after transfer, prolyl peptide bonds in substrate proteins are isomerized very rapidly. The Michaelis constant of catalyzed folding reflects the substrate affinity of the chaperone domain, and the turnover number is presumably determined by the rate of productive substrate transfer from the chaperone to the prolyl isomerase site and by the intrinsic propensity of the refolding protein chain to leave the active site with the native prolyl isomer. The efficiency of substrate transfer is high because dissociation from the chaperone site is very fast and because the two sites are close to each other. Protein molecules that left the prolyl isomerase site with an incorrect prolyl isomer can rapidly be re-bound by the chaperone domain because the association rate is very high as well.
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ABSTRACT: ABSTRACT SurA is a component of the periplasmic chaperone network that plays a central role in biogenesis of integral outer membrane β-barrel proteins (OMPs) in Escherichia coli. Although SurA contains two well-conserved proline isomerase (PPIase) domains, the contribution of these domains to SurA function is unclear. In the present work, we show that defects in OMP assembly caused by mutation of the β-barrel assembly factors BamA or BamB can be corrected by gain-of-function mutations in SurA that map to the first PPIase domain. These mutations apparently bypass the requirement for a stable interaction between SurA and the Bam complex and enhance SurA chaperone activity in vivo despite destabilization of the protein in vitro. Our findings suggest an autoinhibitory mechanism for regulation of SurA chaperone activity through interdomain interactions involving a PPIase domain. We propose a model in which SurA activity is modulated by an interaction between SurA and the Bam complex that alters the substrate specificity of the chaperone. IMPORTANCE The dominant surA mutations described here alter amino acid residues that are highly conserved in eukaryotic homologs of SurA, including Pin1, the human proline isomerase (PPIase) implicated in Alzheimer's disease and certain cancers. Consequently, a mechanistic description of SurA function may enhance our understanding of clinically important PPIases and their role(s) in disease. In addition, the virulence of Gram-negative bacterial pathogens, such as Salmonella, Shigella, and Escherichia coli O157:H7, is largely dependent on SurA, making this PPIase/chaperone an attractive antibiotic target. Investigating the function of SurA in outer membrane (OM) biogenesis will be useful in the development of novel therapeutic strategies for the disruption of the OM or the processes that are essential for its assembly.mBio 06/2013; 4(4). DOI:10.1128/mBio.00540-13 · 6.88 Impact Factor
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ABSTRACT: Prolyl cis/trans isomerizations have long been known as critical and rate-limiting steps in protein folding. More recently, it became clear that they are also used as slow conformational switches and molecular timers in the regulation of protein activity. Here we describe several such proline switches, how they are regulated and how prolyl isomerizations can function as attenuators and provide allosteric systems with a molecular memory. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.Biochimica et Biophysica Acta (BBA) - General Subjects 12/2014; DOI:10.1016/j.bbagen.2014.12.019 · 3.83 Impact Factor
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ABSTRACT: Prolyl isomerizations are intrinsically slow processes. They determine the rates of many protein folding reactions and control regulatory events in folded proteins. Prolyl isomerases are able to catalyze these isomerizations, and thus they have the potential to assist protein folding and to modulate protein function. Here we provide examples for how prolyl isomerizations limit protein folding and are accelerated by prolyl isomerases, and how native-state prolyl isomerizations regulate protein functions. The roles of prolines in protein folding and protein function are closely interrelated because they both depend on the coupling between cis/trans isomerization and conformational changes that can involve extended regions of a protein. Copyright © 2015. Published by Elsevier Ltd.Journal of Molecular Biology 02/2015; DOI:10.1016/j.jmb.2015.01.023 · 3.96 Impact Factor