A filamentous molecular chaperone of the prefoldin family from the deep-sea hyperthermophile Methanocaldococcus jannaschii

A Self-Assembling γPFD-SpyCatcher Hydrogel Scaffold for the Coimmobilization of SpyTag-Enzymes to Facilitate the Catalysis of Regulated Enzymes

In this study, a γPFD-SpyCatcher hydrogel scaffold with the capacity for spontaneous assembly was established. With a maximum loading capacity of a 1:1 molar ratio with SpyTag-enzymes, the immobilized proteins can not only rapidly provide pure enzymes but also exhibit improved thermal and pH stability. The results of the transmission electron microscopic analysis and the traits they present indicated that SpyCatcher promotes the aggregation of γPFD and the formation of hydrogels. In the cell-free pyruvate synthesis system, the γPFD-SpyCatcher coimmobilized SpyTag-hexokinase (HK), SpyTag-phosphofructokinase (PFK) and SpyTag-pyruvate kinase (PK) were employed, and the production of pyruvate increased by 43, 78 and 47% respectively. In in vitro experiments, the oxidative deamination activity of glutamate dehydrogenase (GDH) coimmobilized with γPFD-SpyCatcher was 38% higher than that of purified enzymes. These findings indicate that the γPFD-SpyCatcher-based hydrogels play an important role in breaking the barrier of regulatory enzymes and will provide more strategies for the development of synthetic biology.

Coupling protein scaffold and biosilicification: A sustainable and recyclable approach for d-mannitol production via one-step purification and immobilization of multienzymes

Enzymatic synthesis of biochemicals in vitro is vital in synthetic biology for its efficiency, minimal by-products, and easy product separation. However, challenges like enzyme preparation, stability, and reusability persist. Here, we introduced a protein scaffold and biosilicification coupled system, providing a singular process for the purification and immobilization of multiple enzymes. Using d-mannitol as a model, we initially constructed a self-assembling EE/KK protein scaffold for the co-immobilization of glucose dehydrogenase and mannitol dehydrogenase. Under an enzyme-to-scaffold ratio of 1:8, a d-mannitol yield of 0.692 mol/mol was achieved within 4 h, 2.16-fold higher than the free enzymes. The immobilized enzymes retained 70.9 % of the initial joint activity while the free ones diminished nearly to inactivity after 8 h. Furthermore, we incorporated the biosilicification peptide CotB into the EE/KK scaffold, inducing silica deposition, which enabled the one-step purification and immobilization process assisted by Spy/Snoop protein-peptide pairs. The coupled system demonstrated a comparable d-mannitol yield to that of EE/KK scaffold and 1.34-fold higher remaining activities after 36 h. Following 6 cycles of reaction, the immobilized system retained the capability to synthesize 56.4 % of the initial d-mannitol titer. The self-assembly co-immobilization platform offers an effective approach for enzymatic synthesis of d-mannitol and other biochemicals.

STORM Super-Resolution Visualization of Self-Assembled γPFD Chaperone Ultrastructures in Methanocaldococcus jannaschii

Gamma-prefoldin (γPFD), a unique chaperone found in the extremely thermophilic methanogen Methanocaldococcus jannaschii, self-assembles into filaments in vitro, which so far have been observed using transmission electron microscopy and cryo-electron microscopy. Utilizing three-dimensional stochastic optical reconstruction microscopy (3D-STORM), here we achieve ∼20 nm resolution by precisely locating individual fluorescent molecules, hence resolving γPFD ultrastructure both in vitro and in vivo. Through CF647 NHS ester labeling, we first demonstrate the accurate visualization of filaments and bundles with purified γPFD. Next, by implementing immunofluorescence labeling after creating a 3xFLAG-tagged γPFD strain, we successfully visualize γPFD in M. jannaschii cells. Through 3D-STORM and two-color STORM imaging with DNA, we show the widespread distribution of filamentous γPFD structures within the cell. These findings provide valuable insights into the structure and localization of γPFD, opening up possibilities for studying intriguing nanoscale components not only in archaea but also in other microorganisms.

Prefoldin 2 contributes to mitochondrial morphology and function

BACKGROUND

Prefoldin is an evolutionarily conserved co-chaperone of the tailless complex polypeptide 1 ring complex (TRiC)/chaperonin containing tailless complex 1 (CCT). The prefoldin complex consists of six subunits that are known to transfer newly produced cytoskeletal proteins to TRiC/CCT for folding polypeptides. Prefoldin function was recently linked to the maintenance of protein homeostasis, suggesting a more general function of the co-chaperone during cellular stress conditions. Prefoldin acts in an adenosine triphosphate (ATP)-independent manner, making it a suitable candidate to operate during stress conditions, such as mitochondrial dysfunction. Mitochondrial function depends on the production of mitochondrial proteins in the cytosol. Mechanisms that sustain cytosolic protein homeostasis are vital for the quality control of proteins destined for the organelle and such mechanisms among others include chaperones.

RESULTS

We analyzed consequences of the loss of prefoldin subunits on the cell proliferation and survival of Saccharomyces cerevisiae upon exposure to various cellular stress conditions. We found that prefoldin subunits support cell growth under heat stress. Moreover, prefoldin facilitates the growth of cells under respiratory growth conditions. We showed that mitochondrial morphology and abundance of some respiratory chain complexes was supported by the prefoldin 2 (Pfd2/Gim4) subunit. We also found that Pfd2 interacts with Tom70, a receptor of mitochondrial precursor proteins that are targeted into mitochondria.

CONCLUSIONS

Our findings link the cytosolic prefoldin complex to mitochondrial function. Loss of the prefoldin complex subunit Pfd2 results in adaptive cellular responses on the proteome level under physiological conditions suggesting a continuous need of Pfd2 for maintenance of cellular homeostasis. Within this framework, Pfd2 might support mitochondrial function directly as part of the cytosolic quality control system of mitochondrial proteins or indirectly as a component of the protein homeostasis network.

Harnessing the Structural and Functional Diversity of Protein Filaments as Biomaterial Scaffolds

The natural ability of many proteins to polymerize into highly structured filaments has been harnessed as scaffolds to align functional molecules in a diverse range of biomaterials. Protein-engineering methodologies also enable the structural and physical properties of filaments to be tailored for specific biomaterial applications through genetic engineering or filaments built from the ground up using advances in the computational prediction of protein folding and assembly. Using these approaches, protein filament-based biomaterials have been engineered to accelerate enzymatic catalysis, provide routes for the biomineralization of inorganic materials, facilitate energy production and transfer, and provide support for mammalian cells for tissue engineering. In this review, we describe how the unique structural and functional diversity in natural and computationally designed protein filaments can be harnessed in biomaterials. In addition, we detail applications of these protein assemblies as material scaffolds with a particular emphasis on applications that exploit unique properties of specific filaments. Through the diversity of protein filaments, the biomaterial engineer's toolbox contains many modular protein filaments that will likely be incorporated as the main structural component of future biomaterials.

Prefoldin Function in Cellular Protein Homeostasis and Human Diseases

Cellular functions are largely performed by proteins. Defects in the production, folding, or removal of proteins from the cell lead to perturbations in cellular functions that can result in pathological conditions for the organism. In cells, molecular chaperones are part of a network of surveillance mechanisms that maintains a functional proteome. Chaperones are involved in the folding of newly synthesized polypeptides and assist in refolding misfolded proteins and guiding proteins for degradation. The present review focuses on the molecular co-chaperone prefoldin. Its canonical function in eukaryotes involves the transfer of newly synthesized polypeptides of cytoskeletal proteins to the tailless complex polypeptide 1 ring complex (TRiC/CCT) chaperonin which assists folding of the polypeptide chain in an energy-dependent manner. The canonical function of prefoldin is well established, but recent research suggests its broader function in the maintenance of protein homeostasis under physiological and pathological conditions. Interestingly, non-canonical functions were identified for the prefoldin complex and also for its individual subunits. We discuss the latest findings on the prefoldin complex and its subunits in the regulation of transcription and proteasome-dependent protein degradation and its role in neurological diseases, cancer, viral infections and rare anomalies.

A comprehensive analysis of prefoldins and their implication in cancer

Prefoldins (PFDNs) are evolutionary conserved co-chaperones, initially discovered in archaea but universally present in eukaryotes. PFDNs are prevalently organized into hetero-hexameric complexes. Although they have been overlooked since their discovery and their functions remain elusive, several reports indicate they act as co-chaperones escorting misfolded or non-native proteins to group II chaperonins. Unlike the eukaryotic PFDNs which interact with cytoskeletal components, the archaeal PFDNs can bind and stabilize a wide range of substrates, possibly due to their great structural diversity. The discovery of the unconventional RPB5 interactor (URI) PFDN-like complex (UPC) suggests that PFDNs have versatile functions and are required for different cellular processes, including an important role in cancer. Here, we summarize their functions across different species. Moreover, a comprehensive analysis of PFDNs genomic alterations across cancer types by using large-scale cancer genomic data indicates that PFDNs are a new class of non-mutated proteins significantly overexpressed in some cancer types.

Filamentous chaperone protein-based hydrogel stabilizes enzymes against thermal inactivation

We report a filamentous chaperone-based protein hydrogel capable of stabilizing enzymes against thermal inactivation. The hydrogel backbone consists of a thermostable chaperone protein, the gamma-prefoldin (γPFD) from Methanocaldococcus jannaschii, which self-assembles into a fibrous structure. Specific coiled-coil interactions engineered into the wildtype γPFD trigger the formation of a cross-linked network of protein filaments. The structure of the filamentous chaperone is preserved through the designed coiled-coil interactions. The resulting hydrogel enables entrapped enzymes to retain greater activity after exposure to high temperatures, presumably by virtue of the inherent chaperone activity of the γPFD.

Enhanced Production of Soluble Pyrococcus furiosus α-Amylase in Bacillus subtilis through Chaperone Co-Expression, Heat Treatment and Fermentation Optimization

Pyrococcus furiosus α-amylase can hydrolyze α-1,4 linkages in starch and related carbohydrates under hyperthermophilic condition (~ 100°C), showing great potential in a wide range of industrial applications, while its relatively low productivity from heterologous hosts has limited the industrial applications. Bacillus subtilis, a gram-positive bacterium, has been widely used in industrial production for its non-pathogenic and powerful secretory characteristics. This study was conducted to increase production of P. furiosus α-amylase in B. subtilis through three strategies. Initial experiments showed that co-expression of P. furiosus molecular chaperone peptidyl-prolyl cis-trans isomerase through genomic integration mode, using a CRISPR/Cas9 system, increased soluble amylase production. Therefore, considering that native P. furiosus α-amylase is produced within a hyperthermophilic environment and is highly thermostable, heat treatment of intact culture at 90°C for 15 min was performed, thereby greatly increasing soluble amylase production. After optimization of the culture conditions (nitrogen source, carbon source, metal ion, temperature and pH), experiments in a 3-L fermenter yielded a soluble activity of 3,806.7 U/ml, which was 3.3- and 28.2-fold those of a control without heat treatment (1,155.1 U/ml) and an empty expression vector control (135.1 U/ml), respectively. This represents the highest P. furiosus α-amylase production reported to date and should promote innovation in the starch liquefaction process and related industrial productions. Meanwhile, heat treatment, which may promote folding of aggregated P. furiosus α-amylase into a soluble, active form through the transfer of kinetic energy, may be of general benefit when producing proteins from thermophilic archaea.

Comparative structural insight into prefoldin subunints of archaea and eukaryotes with special emphasis on unexplored prefoldin of Plasmodium falciparum

Prefoldin (PFD) is a heterohexameric molecular chaperone which bind unfolded proteins and subsequently deliver them to a group II chaperonin for correct folding. Although there is structural and functional information available for humans and archaea PFDs, their existence and functions in malaria parasite remains uncharacterized. In the present review, we have collected the available information on prefoldin family members of archaea and humans and attempted to analyze unexplored PFD subunits of Plasmodium falciparum (Pf). Our review enhances the understanding of probable functions, structure and mechanism of substrate binding of Pf prefoldin by comparing with the available information of its homologs in archaea and H. sapiens. Three PfPFD out of six and a Pf prefoldin-like protein are reported to be essential for parasite survival that signifies their importance in malaria parasite biology. Transcriptome analyses suggest that PfPFD subunits are up-regulated at the mRNA level during asexual and sexual stages of parasite life cycle. Our in silico analysis suggested several pivotal proteins like myosin E, cytoskeletal protein (tubulin), merozoite surface protein and ring exported protein 3 as their interacting partners. Based on structural information of archaeal and H. sapiens PFDs, P. falciparum counterparts have been modelled and key interface residues were identified that are critical for oligomerization of PfPFD subunits. We collated information on PFD-substrate binding and PFD-chaperonin interaction in detail to understand the mechanism of substrate delivery in archaea and humans. Overall, our review enables readers to view the PFD family comprehensively. Communicated by Ramaswamy H. SarmaAbbreviations: HSP: Heat shock proteins; CCT: Chaperonin containing TCP-1; PFD: Prefoldin; PFLP: Prefoldin like protein; PfPFD: Plasmodium falciparum prefoldin; Pf: Plasmodium falciparum; H. sapiens: Homo sapiens; M. thermoautotrophicus: Methanobacterium thermoautotrophicus; P. horikoshii: Pyrococcus horikoshii.

The functions and mechanisms of prefoldin complex and prefoldin-subunits

The correct folding is a key process for a protein to acquire its functional structure and conformation. Prefoldin is a well-known chaperone protein that regulates the correct folding of proteins. Prefoldin plays a crucial role in the pathogenesis of common neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, and Huntington's disease). The important role of prefoldin in emerging fields (such as nanoparticles, biomaterials) and tumors has attracted widespread attention. Also, each of the prefoldin subunits has different and independent functions from the prefoldin complex. It has abnormal expression in different tumors and plays an important role in tumorigenesis and development, especially c-Myc binding protein MM-1. MM-1 can inhibit the activity of c-Myc through various mechanisms to regulate tumor growth. Therefore, an in-depth analysis of the complex functions of prefoldin and their subunits is helpful to understand the mechanisms of protein misfolding and the pathogenesis of diseases caused by misfolded aggregation.

Structural Determination of a Filamentous Chaperone to Fabricate Electronically Conductive Metalloprotein Nanowires

The transfer of electrons through protein complexes is central to cellular respiration. Exploiting proteins for charge transfer in a controllable fashion has the potential to revolutionize the integration of biological systems and electronic devices. Here we characterize the structure of an ultrastable protein filament and engineer the filament subunits to create electronically conductive nanowires under aqueous conditions. Cryoelectron microscopy was used to resolve the helical structure of gamma-prefoldin, a filamentous protein from a hyperthermophilic archaeon. Conjugation of tetra-heme c3-type cytochromes along the longitudinal axis of the filament created nanowires capable of long-range electron transfer. Electrochemical transport measurements indicated networks of the nanowires capable of conducting current between electrodes at the redox potential of the cytochromes. Functionalization of these highly engineerable nanowires with other molecules, such as redox enzymes, may be useful for bioelectronic applications.

Production of Multicomponent Protein Templates for the Positioning and Stabilization of Enzymes

Harnessing the ability of proteins to self-assemble into complex structures has enabled the creation of templates for applications in nanotechnology. Protein templates can be used to position functional molecules in regular patterns with nanometer precision over large surface areas. A difficult but successful approach to building customizable protein templates involves designing novel protein-protein interfaces to join protein building blocks into ordered arrangements. This approach was illustrated recently by engineering the protein interfaces of a molecular chaperone to produce filamentous templates composed of repeating subunits. In this chapter, we describe how these multicomponent protein templates can be produced recombinantly, assembled into filaments, and used as material templates. The templates enable the positioning and alignment of functional molecules at varying distances along the length of the filament, which can be demonstrated using a Förster resonance energy transfer (FRET) assay. In addition, we describe a method to quantify the chaperone ability of these filaments to stabilize and protect other proteins from thermal-induced aggregation-a useful property for bionanotechnology applications that involve molecular scaffolds for positioning and stabilizing enzymes.

Enhanced Enzyme Activity through Scaffolding on Customizable Self-Assembling Protein Filaments

Precisely organized enzyme complexes are often found in nature to support complex metabolic reactions in a highly efficient and specific manner. Scaffolding enzymes on artificial materials has thus gained attention as a promising biomimetic strategy to design biocatalytic systems with enhanced productivity. Herein, a versatile scaffolding platform that can immobilize enzymes on customizable nanofibers is reported. An ultrastable self-assembling filamentous protein, the gamma-prefoldin (γ-PFD), is genetically engineered to display an array of peptide tags, which can specifically and stably bind enzymes containing the counterpart domain through simple in vitro mixing. Successful immobilization of proteins along the filamentous template in tunable density is first verified using fluorescent proteins. Then, two different model enzymes, glucose oxidase and horseradish peroxidase, are used to demonstrate that scaffold attachment could enhance the intrinsic catalytic activity of the immobilized enzymes. Considering the previously reported ability of γ-PFD to bind and stabilize a broad range of proteins, the filament's interaction with the bound enzymes may have created a favorable microenvironment for catalysis. It is envisioned that the strategy described here may provide a generally applicable methodology for the scaffolded assembly of multienzymatic complexes for use in biocatalysis.

Controlled Assembly of the Filamentous Chaperone Gamma-Prefoldin into Defined Nanostructures

Self-assembling protein templates have enormous potential for the fabrication of multifunctional nanostructures that require precise positioning of individual molecules, such as enzymes and inorganic moieties, in regular patterns. A recently described approach uses ultrastable filaments composed of the gamma-prefoldin (γPFD) protein and engineered connector proteins to construct novel architectures useful for basic research and practical applications in nanobiotechnology. Here we describe the production of the γPFD and connector proteins from E. coli, and the assembly of γPFD with connector proteins into macromolecular structures with defined shapes.

Engineering bioorthogonal protein-polymer hybrid hydrogel as a functional protein immobilization platform

We demonstrate the synthesis of protein-polymer hybrid hydrogel that can be used as a platform for immobilizing functional proteins. Orthogonal chemistry was employed for cross-linking the hybrid network and conjugating proteins to the gel backbone, allowing for the convenient, one-pot formation of a functionalized hydrogel. The resulting hydrogel had tunable mechanical properties, was stable in solution, and biocompatible.

Prefoldins in Archaea

Molecular chaperones promote the correct folding of proteins in aggregation-prone cellular environments by stabilizing nascent polypeptide chains and providing appropriate folding conditions. Prefoldins (PFDs) are molecular chaperones found in archaea and eukaryotes, generally characterized by a unique jellyfish-like hexameric structure consisting of a rigid beta-barrel backbone with protruding flexible coiled-coils. Unlike eukaryotic PFDs that mainly interact with cytoskeletal components, archaeal PFDs can stabilize a wide range of substrates; such versatility reflects PFD's role as a key element in archaeal chaperone systems, which often lack general nascent-chain binding chaperone components such as Hsp70. While archaeal PFDs mainly exist as hexameric complexes, their structural diversity ranges from tetramers to filamentous oligomers. PFDs bind and stabilize nonnative proteins using varying numbers of coiled-coils, and subsequently transfer the substrate to a group II chaperonin (CPN) for refolding. The distinct structure and specific function of archaeal PFDs have been exploited for a broad range of applications in biotechnology; furthermore, a filament-forming variant of PFD has been used to fabricate nanoscale architectures of defined shapes, demonstrating archaeal PFDs' potential applicability in nanotechnology.

The proteome map of the escamolera ant (Liometopum apiculatum Mayr) larvae reveals immunogenic proteins and several hexamerin proteoforms

The larvae of escamolera ant (Liometopum apiculatum Mayr) have been considered a delicacy since Pre-Hispanic times. The increased demand for this stew has led to massive collection of ant nests. Yet biological aspects of L. apiculatum larvae remain unknown, and mapping the proteome of this species is important for understanding its biological characteristics. Two-dimensional gel electrophoresis (2-DE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was used to characterize the larvae proteome profile. From 380 protein spots analyzed, 174 were identified by LC-MS/MS and homology search against the Hymenoptera subset of the NCBInr protein database using the Mascot search engine. Peptide de novo sequencing and homology-based alignment allowed the identification of 36 additional protein spots. Identified proteins were classified by cellular location, molecular function, and biological process according to the Gene Ontology annotation. Immunity- and defense-related proteins were identified including PPIases, FK506, PEBP, and chitinases. Several hexamerin proteoforms were identified and the cDNA of the most abundant protein detected in the 2-DE map was isolated and characterized. L. apiculatum hexamerin (LaHEX, GeneBank accession no. MH256667) contains an open reading frame of 2199 bp encoding a polypeptide of 733 amino acid residues with a calculated molecular mass of 82.41 kDa. LaHEX protein is more similar to HEX110 than HEX70 from Apis mellifera. Down-regulation of LaHEX was observed throughout ant development. This work represents the first proteome map as well as the first hexamerin characterized from L. apiculatum larvae.

Prefoldin, a jellyfish-like molecular chaperone: functional cooperation with a group II chaperonin and beyond

Prefoldin is a hexameric molecular chaperone found in the cytosol of archaea and eukaryotes. Its hexameric complex is built from two related classes of subunits and has the appearance of a jellyfish: its body consists of a double beta-barrel assembly with six long tentacle-like coiled coils protruding from it. Using the tentacles, prefoldin captures an unfolded protein substrate and transfers it to a group II chaperonin. The prefoldin-group II chaperonin system is thought to be important for the folding of newly synthesized proteins and for their maintenance, or proteostasis, in the cytosol. Based on structural information of archaeal prefoldins, the mechanisms of substrate recognition and prefoldin-chaperonin cooperation have been investigated. In contrast, the role and mechanism of eukaryotic PFDs remain unknown. Recent studies have shown that prefoldin plays an important role in proteostasis and is involved in various diseases. In this paper, we review a series of studies on the molecular mechanisms of archaeal prefoldins and introduce recent findings about eukaryotic prefoldin.

Structure and Function of the Cochaperone Prefoldin

Molecular chaperones are key players in proteostasis, the balance between protein synthesis, folding, assembly and degradation. They are helped by a plethora of cofactors termed cochaperones, which direct chaperones towards any of these different, sometime opposite pathways. One of these is prefoldin (PFD), present in eukaryotes and in archaea, a heterohexamer whose best known role is the assistance to group II chaperonins (the Hsp60 chaperones found in archaea and the eukaryotic cytosolic) in the folding of proteins in the cytosol, in particular cytoskeletal proteins. However, over the last years it has become evident a more complex role for this cochaperone, as it can adopt different oligomeric structures, form complexes with other proteins and be involved in many other processes, both in the cytosol and in the nucleus, different from folding. This review intends to describe the structure and the many functions of this interesting macromolecular complex.

Molecular chaperones: functional mechanisms and nanotechnological applications

Molecular chaperones are a group of proteins that assist in protein homeostasis. They not only prevent protein misfolding and aggregation, but also target misfolded proteins for degradation. Despite differences in structure, all types of chaperones share a common general feature, a surface that recognizes and interacts with the misfolded protein. This and other, more specialized properties can be adapted for various nanotechnological purposes, by modification of the original biomolecules or by de novo design based on artificial structures.

Geometrical assembly of ultrastable protein templates for nanomaterials

The fabrication of nanoscale devices requires architectural templates on which to position functional molecules in complex arrangements. Protein scaffolds are particularly promising templates for nanomaterials due to inherent molecular recognition and self-assembly capabilities combined with genetically encoded functionalities. However, difficulties in engineering protein quaternary structure into stable and well-ordered shapes have hampered progress. Here we report the development of an ultrastable biomolecular construction kit for the assembly of filamentous proteins into geometrically defined templates of controllable size and symmetry. The strategy combines redesign of protein–protein interaction specificity with the creation of tunable connector proteins that govern the assembly and projection angles of the filaments. The functionality of these nanoarchitectures is illustrated by incorporation of nanoparticles at specific locations and orientations to create hybrid materials such as conductive nanowires. These new structural components facilitate the manufacturing of nanomaterials with diverse shapes and functional properties over a wide range of processing conditions.

Protein nanotechnology for the fabrication of protein-based nanoscale devices is gaining momentum but assembling well-defined three-dimensional shapes is still challenging. Here, the authors use an existing prefoldin assembled system to design a template for the construction of geometrically constrained structures.

Rational shape engineering of the filamentous protein gamma prefoldin through incremental gene truncation

An enticing possibility in nanotechnology is to use proteins as templates for the positioning of molecules in regular patterns with nanometer precision over large surface areas. However, the ability to redesign protein quaternary structure to construct new shapes remains underdeveloped. In the present work, we have engineered the dimensions of a filamentous protein, the gamma prefoldin (gamma PFD) from the hyperthermophile Methanocaldococcus jannaschii, and have achieved controllable attachment of filaments in a specific orientation on a carbon surface. Four different constructs of gamma PFD were generated in which the coiled coils extending from the association domain are progressively truncated. Three of the truncation constructs form well-defined filaments with predictable dimensions according to transmission electron microscopy. Two of these constructs had 2D persistence lengths similar to that of gamma PFD at 300-740 nm. In contrast, the 2D persistence length of the shortest truncation mutant was 3500 nm, indicating that the filament adsorbs along a different axis than the other constructs with its two rows of coiled coils facing out from the surface. The elastic moduli of the filaments range from 0.7-2.1 GPa, similar to rigid plastics and within the lower limit for proteins whose primary intermolecular interaction is hydrogen bonding. These results demonstrate a versatile approach for controlling the overall dimensions and surface orientation of protein filaments, and expand the toolbox by which to tune two overall dimensions in protein space for the creation of templated materials over a wide variety of conditions. (c) 2009 Wiley Periodicals, Inc. Biopolymers 91: 496-503, 2009.

Kinetic control of histidine-tagged protein surface density on supported lipid bilayers

Nickel-chelating lipids are general tools for anchoring polyhistidine-tagged proteins to supported lipid bilayers (SLBs), but controversy exists over the stability of the protein-lipid attachment. Here, we show that chelator lipids are suitable anchors for building stable, biologically active surfaces but that a simple Langmuirian model is insufficient to describe their behavior. Desorption kinetics from chelator lipids are governed by the valency of surface binding: monovalently bound proteins desorb within minutes (t1/2 approximately 6 min), whereas polyvalently bound species remain bound for hours (t1/2 approximately 12 h). Evolution between surface states is slow, so equilibrium is unlikely to be reached on experimental timescales. However, by tuning incubation conditions, the populations of each species can be kinetically controlled, providing a wide range of protein densities on SLBs with a single concentration of chelator lipid. We propose guidelines for the assembly of SLB surfaces functionalized with specific protein densities and demonstrate their utility in the formation of hybrid immunological synapses.

Chaperone function in organic co-solvents: experimental characterization and modeling of a hyperthermophilic chaperone subunit from Methanocaldococcus jannaschii

Molecular chaperones play a central role in maintaining protein structure within a cell. Previously, we determined that the gene encoding a molecular chaperone, a thermosome, from the hyperthermophilic archaeon Methanocaldococcus jannaschii is upregulated upon lethal heat shock. We have recombinantly expressed this thermosome (rTHS) and show here that it is both stable and fully functional in aqueous solutions containing water-miscible organic co-solvents. Based on circular dichroism the secondary structure of rTHS was not affected by one-hour exposures to a variety of co-solvents including 30% v/v acetonitrile (ACN) and 50% methanol (MeOH). By contrast, the secondary structure of a mesophilic homologue, GroEL/GroES (GroE), was substantially disrupted. rTHS reduced the aggregation of ovalbumin and citrate synthase in 30% ACN, assisted refolding of citrate synthase upon solvent-inactivation, and stabilized citrate synthase and glutamate dehydrogenase in the direct presence of co-solvents. Apparent total turnover numbers of these enzymes in denaturing solutions increased by up to 2.5-fold in the presence of rTHS. Mechanistic models are proposed to help ascertain specific conditions that could enhance or limit organic solvent-induced chaperone activity. These models suggest that thermodynamic stability and the reversibility of enzyme unfolding play key roles in the effectiveness of enzyme recovery by rTHS.