De novo design of a reversible phosphorylation-dependent switch for membrane targeting

A de novo designed coiled coil-based switch regulates the microtubule motor kinesin-1

Many enzymes are allosterically regulated via conformational change; however, our ability to manipulate these structural changes and control function is limited. Here we install a conformational switch for allosteric activation into the kinesin-1 microtubule motor in vitro and in cells. Kinesin-1 is a heterotetramer that accesses open active and closed autoinhibited states. The equilibrium between these states centers on a flexible elbow within a complex coiled-coil architecture. We target the elbow to engineer a closed state that can be opened with a de novo designed peptide. The alternative states are modeled computationally and confirmed by biophysical measurements and electron microscopy. In cells, peptide-driven activation increases kinesin transport, demonstrating a primary role for conformational switching in regulating motor activity. The designs are enabled by our understanding of ubiquitous coiled-coil structures, opening possibilities for controlling other protein activities.

The impact of IDR phosphorylation on the RNA binding profiles of proteins

Due to their capacity to mediate repetitive protein interactions, intrinsically disordered regions (IDRs) are crucial for the formation of various types of protein-RNA complexes. The functions of IDRs are strongly modulated by post-translational modifications (PTMs). Phosphorylation is the most common and well-studied modification of IDRs, which can alter homomeric or heteromeric interactions of proteins and impact their ability to phase separate. Moreover, phosphorylation can influence the RNA-binding properties of proteins, and recent studies demonstrated its selective impact on the global profiles of protein-RNA binding and regulation. These findings highlight the need for further integrative approaches to understand how signalling remodels protein-RNA networks in cells.

Protein Interaction Kinetics Delimit the Performance of Phosphorylation-Driven Protein Switches

Post-translational modifications (PTMs) such as phosphorylation and dephosphorylation can rapidly alter protein surface chemistry and structural conformation, which can switch protein-protein interactions (PPIs) within signaling networks. Recently, de novo-designed phosphorylation-responsive protein switches have been created that harness kinase- and phosphatase-mediated phosphorylation to modulate PPIs. PTM-driven protein switches are promising tools for investigating PTM dynamics in living cells, developing biocompatible nanodevices, and engineering signaling pathways to program cell behavior. However, little is known about the physical and kinetic constraints of PTM-driven protein switches, which limits their practical application. In this study, we present a framework to evaluate two-component PTM-driven protein switches based on four performance metrics: effective concentration, dynamic range, response time, and reversibility. Our computational models reveal an intricate relationship between the binding kinetics, phosphorylation kinetics, and switch concentration that governs the sensitivity and reversibility of PTM-driven protein switches. Building upon the insights of the interaction modeling, we built and evaluated novel phosphorylation-driven protein switches consisting of phosphorylation-sensitive coiled coils as sensor domains fused to fluorescent proteins as actuator domains. By modulating the phosphorylation state of the switches with a specific protein kinase and phosphatase, we demonstrate fast, reversible transitions between "on" and "off" states. The response of the switches linearly correlated to the kinase concentration, demonstrating its potential as a biosensor for kinase measurements in real time. As intended, the switches responded to specific kinase activity with an increase in the fluorescence signal and our model could be used to distinguish between two mechanisms of switch activation: dimerization or a structural rearrangement. The protein switch kinetics model developed here should enable PTM-driven switches to be designed with ideal performance for specific applications.

Computation-Driven Rational Design of Self-Assembled Short Peptides for Catalytic Hydrogen Production

Self-assembling peptides represent a captivating area of study in nanotechnology and biomaterials. This interest is largely driven by their unique properties and the vast application potential across various fields such as catalytic functions. However, design complexities, including high-dimensional sequence space and structural diversity, pose significant challenges in the study of such systems. In this work, we explored the possibility of self-assembled peptides to catalyze the hydrolysis of hydrosilane for hydrogen production using ab initio calculations and carried out wet-lab experiments to confirm the feasibility of these catalytic reactions under ambient conditions. Further, we delved into the nuanced interplay between sequence, structural conformation, and catalytic activity by combining modeling with experimental techniques such as transmission electron microscopy and nuclear magnetic resonance and proposed a dual mode of the microstructure of the catalytic center. Our results reveal that although research in this area is still at an early stage, the development of self-assembled peptide catalysts for hydrogen production has the potential to provide a more sustainable and efficient alternative to conventional hydrogen production methods. In addition, this work also demonstrates that a computation-driven rational design supplemented by experimental validation is an effective protocol for conducting research on functional self-assembled peptides.

Enzyme-Driven, Switchable Catalysis Based on Dynamic Self-Assembly of Peptides

Covalent regulatory systems of enzymes are widely used to modulate biological enzyme activities. Inspired by the regulation of reactive-site phosphorylation in organisms, we developed peptide-based catecholase mimetics with switchable catalytic activity and high selectivity through the co-assembly of nanofibers comprising peptides and copper ions (Cu2+ ). Through careful design and modification of the peptide backbone structure based on the change in the free energy of the system, we identified the peptide with the most effective reversible catalytic activity. Kinase/phosphatase switches were used to control the reversible transition of nanofiber formation and depolymerization, as well as to modulate the active-site microenvironment. Notably, the self-assembly and disassembly processes of nanofibers were simulated using coarse-grained molecular dynamics. Furthermore, theoretical calculations confirmed the coordination of the peptide and Cu2+ , forming a zipper-like four-ligand structure at the catalytically active center of the nanofibers. Additionally, we conducted a comprehensive analysis of the catalytic mechanism. This study opens novel avenues for designing biomimetic enzymes with ordered structures and dynamic catalytic activities.

Quantitative phosphoproteomics reveals molecular pathway network alterations in human early-stage primary hepatic carcinomas: potential for 3P medical approach

Objective

Hepatic carcinoma is one of the most common types of malignant tumors in the digestive system, and its biological characteristics determine its high rate of metastasis and recurrence after radical resection, leading to a poor prognosis for patients. Increasing evidence demonstrates that phosphoproteins and phosphorylation-mediated molecular pathways influence the occurrence and development of hepatic carcinoma. It is urgent need to develop early-stage biomarkers for improving diagnosis, therapy, medical service, and prognostic assessment. We hypothesize that phosphoproteome and phosphorylation-mediated signaling pathway networks significantly differ in human early-stage primary hepatic carcinomas relative to control liver tissues, which will identify the key differentially phosphorylated proteins and phosphorylation-mediated signaling pathway network alterations in human early-stage primary hepatic carcinoma to innovate predictive diagnosis, prognostic assessment, and personalized medical services and progress beyond the state of the art in the framework of predictive, preventive, and personalized medicine (PPPM).

Methods

Tandem mass tag (TMT)-based quantitative proteomics coupled with TiO2 enrichment of phosphopeptides was used to identify phosphorylation profiling, and bioinformatics was used to analyze the pathways and biological functions of phosphorylation profiling between early-stage hepatic carcinoma tissues and tumor-adjacent normal control tissues. Furthermore, the integrative analysis with transcriptomic data from TCGA database obtained differently expressed genes (DEGs) corresponding to differentially phosphorylated proteins (DPPs) and overall survival (OS)-related DPPs.

Results

A total of 1326 phosphopeptides derived from 858 DPPs in human early-stage primary hepatic carcinoma were identified. KEGG pathway network analysis of 858 DPPs revealed 33 statistically significant signaling pathways, including spliceosome, glycolysis/gluconeogenesis, B-cell receptor signaling pathway, HIF-1 signaling pathway, and fatty acid degradation. Gene Ontology (GO) analysis of 858 DPPs revealed that protein phosphorylation was involved in 57 biological processes, 40 cellular components, and 37 molecular functions. Protein-protein interaction (PPI) network constructed multiple high-combined scores and co-expressed DPPs. Integrative analysis of transcriptomic data and DPP data identified 105 overlapped molecules (DPPs; DEGs) between hepatic carcinoma tissues and control tissues and 125 OS-related DPPs. Overlapping Venn plots showed 14 common molecules among datasets of DPPs, DEGs, and OS-related DDPs, including FTCD, NDRG2, CCT2, PECR, SLC23A2, PNPLA7, ANLN, HNRNPM, HJURP, MCM2, STMN1, TCOF1, TOP2A, and SSRP1. The drug sensitivities of OS-related DPPs were identified, including LMOD1, CAV2, UBE2E2, RAPH1, ANXA5, HDLBP, CUEDC1, APBB1IP, VCL, SRSF10, SLC23A2, EPB41L2, ESR1, PLEKHA4, SAFB2, SMARCAD1, VCAN, PSD4, RDH16, NOP56, MEF2C, BAIAP2L2, NAGS, SRSF2, FHOD3, and STMN1.

Conclusions

Identification and annotation of phosphoproteomes and phosphorylation-mediated signaling pathways in human early-stage primary hepatic carcinoma tissues provided new directions for tumor prevention and treatment, which (i) helps to enrich phosphorylation functional research and develop new biomarkers; (ii) enriches phosphorylation-mediated signaling pathways to gain a deeper understanding of the underlying mechanisms of early-stage primary hepatic carcinoma; and (iii) develops anti-tumor drugs that facilitate targeted phosphorylated sites. We recommend quantitative phosphoproteomics in early-stage primary hepatic carcinoma, which offers great promise for in-depth insight into the molecular mechanism of early-stage primary hepatic carcinoma, the discovery of effective therapeutic targets/drugs, and the construction of reliable phosphorylation-related biomarkers for patient stratification, predictive diagnosis, prognostic assessment, and personalized medical services in the framework of PPPM.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13167-023-00335-3.

Lipophilic Anchors that Embed Bioconjugates in Bilayer Membranes: A Review

A wide range of biomaterials and engineered cell surfaces are composed of bioconjugates embedded in liposome membranes, surface-immobilized bilayers, or the plasma membranes of living cells. This review article summarizes the various ways that Nature anchors integral and peripheral proteins in a cell membrane and describes the strategies devised by chemical biologists to label a membrane protein in living cells. Also discussed are modern synthetic and semisynthetic methods to produce lipidated proteins. Subsequent sections describe methods to anchor a three-component synthetic construct that is composed of a lipophilic membrane anchor, hydrophilic linker, and exposed functional component. The surface exposed payload can be a fluorophore, aptamer, oligonucleotide, polypeptide, peptide nucleic acid, polysaccharide, branched dendrimer, or linear polymer. Hydrocarbon chains are commonly used as the membrane anchor, and a general experimental trend is that a two chain lipid anchor has higher membrane affinity than a cholesteryl or single chain lipid anchor. Amphiphilic fluorescent dyes are effective molecular probes for cell membrane imaging and a zwitterionic linker between the fluorophore and the lipid anchor promotes high persistence in the plasma membrane of living cells. A relatively new advance is the development of switchable membrane anchors as molecular tools for fundamental studies or as technology platforms for applied biomaterials.

Design and Selection of Heterodimerizing Helical Hairpins for Synthetic Biology

Synthetic biology applications would benefit from protein modules of reduced complexity that function orthogonally to cellular components. As many subcellular processes depend on peptide-protein or protein-protein interactions, de novo designed polypeptides that can bring together other proteins controllably are particularly useful. Thanks to established sequence-to-structure relationships, helical bundles provide good starting points for such designs. Typically, however, such designs are tested in vitro and function in cells is not guaranteed. Here, we describe the design, characterization, and application of de novo helical hairpins that heterodimerize to form 4-helix bundles in cells. Starting from a rationally designed homodimer, we construct a library of helical hairpins and identify complementary pairs using bimolecular fluorescence complementation in E. coli. We characterize some of the pairs using biophysics and X-ray crystallography to confirm heterodimeric 4-helix bundles. Finally, we demonstrate the function of an exemplar pair in regulating transcription in both E. coli and mammalian cells.

Understanding a protein fold: the physics, chemistry, and biology of α-helical coiled coils

Protein science is being transformed by powerful computational methods for structure prediction and design: AlphaFold2 can predict many natural protein structures from sequence, and other AI methods are enabling the de novo design of new structures. This raises a question: how much do we understand the underlying sequence-to-structure/function relationships being captured by these methods? This perspective presents our current understanding of one class of protein assembly, the α-helical coiled coils. At first sight, these are straightforward: sequence repeats of hydrophobic (h) and polar (p) residues, (hpphppp)_n, direct the folding and assembly of amphipathic α helices into bundles. However, many different bundles are possible: they can have two or more helices (different oligomers); the helices can have parallel, antiparallel or mixed arrangements (different topologies); and the helical sequences can be the same (homomers) or different (heteromers). Thus, sequence-to-structure relationships must be present within the hpphppp repeats to distinguish these states. I discuss the current understanding of this problem at three levels: First, physics gives a parametric framework to generate the many possible coiled-coil backbone structures. Second, chemistry provides a means to explore and deliver sequence-to-structure relationships. Third, biology shows how coiled coils are adapted and functionalized in nature, inspiring applications of coiled coils in synthetic biology. I argue that the chemistry is largely understood; the physics is partly solved, though the considerable challenge of predicting even relative stabilities of different coiled-coil states remains; but there is much more to explore in the biology and synthetic biology of coiled coils.

How phosphorylation impacts intrinsically disordered proteins and their function

Phosphorylation is the most common post-translational modification (PTM) in eukaryotes, occurring particularly frequently in intrinsically disordered proteins (IDPs). These proteins are highly flexible and dynamic by nature. Thus, it is intriguing that the addition of a single phosphoryl group to a disordered chain can impact its function so dramatically. Furthermore, as many IDPs carry multiple phosphorylation sites, the number of possible states increases, enabling larger complexities and novel mechanisms. Although a chemically simple and well-understood process, the impact of phosphorylation on the conformational ensemble and molecular function of IDPs, not to mention biological output, is highly complex and diverse. Since the discovery of the first phosphorylation site in proteins 75 years ago, we have come to a much better understanding of how this PTM works, but with the diversity of IDPs and their capacity for carrying multiple phosphoryl groups, the complexity grows. In this Essay, we highlight some of the basic effects of IDP phosphorylation, allowing it to serve as starting point when embarking on studies into this topic. We further describe how recent complex cases of multisite phosphorylation of IDPs have been instrumental in widening our view on the effect of protein phosphorylation. Finally, we put forward perspectives on the phosphorylation of IDPs, both in relation to disease and in context of other PTMs; areas where deep insight remains to be uncovered.

Reconstitution of a Reversible Membrane Switch via Prenylation by One-Pot Cell-Free Expression

Reversible membrane targeting of proteins is one of the key regulators of cellular interaction networks, for example, for signaling and polarization. So-called "membrane switches" are thus highly attractive targets for the design of minimal cells but have so far been tricky to reconstitute in vitro. Here, we introduce cell-free prenylated protein synthesis (CFpPS), which enables the synthesis and membrane targeting of proteins in a single reaction mix including the prenylation machinery. CFpPS can confer membrane affinity to any protein via addition of a 4-peptide motif to its C-terminus and offers robust production of prenylated proteins not only in their soluble forms but also in the direct vicinity of biomimetic membranes. Thus, CFpPS enabled us to reconstitute the prenylated polarity hub Cdc42 and its regulatory protein in vitro, implementing a key membrane switch. We propose CFpPS to be a versatile and effective platform for engineering complex features, such as polarity induction, in synthetic cells.

Nonequilibrium Amyloid Polymers Exploit Dynamic Covalent Linkage to Temporally Control Charge-Selective Catalysis

Extant proteins exploit thermodynamically activated negatively charged coenzymes and hydrotropes to temporally access mechanistically important conformations that regulate vital biological functions, from metabolic reactions to expression modulation. Herein, we show that a short amyloid peptide can bind to a small molecular coenzyme by exploiting reversible covalent linkage to polymerize and access catalytically proficient nonequilibrium amyloid microphases. Subsequent hydrolysis of the activated coenzyme leads to depolymerization, realizing a variance of the surface charge of the assembly as a function of time. Such temporal change of surface charge dynamically modulates catalytic activities of the transient assemblies as observed in highly evolved modern-day biocatalysts.

Redox- and metal-directed structural diversification in designed metalloprotein assemblies

Herein we describe a designed protein building block whose self-assembly behaviour is dually gated by the redox state of disulphide bonds and the identity of exogenous metal ions. This protein construct is shown - through extensive structural and biophysical characterization - to access five distinct oligomeric states, exemplifying how the complex interplay between hydrophobic, metal-ligand, and reversible covalent interactions could be harnessed to obtain multiple, responsive protein architectures from a single building block.

Engineered Allosteric Regulation of Protein Function

Allosteric regulation of proteins has been utilized to study various aspects of cell signaling, from unicellular events to organism-wide phenotypes. However, traditional methods of allosteric regulation, such as constitutively active mutants and inhibitors, lack tight spatiotemporal control. This often leads to unintended signaling consequences that interfere with data interpretation. To overcome these obstacles, researchers employed protein engineering approaches that enable tight control of protein function through allosteric mechanisms. These methods provide high specificity as well as spatial and temporal precision in regulation of protein activity in vitro and in vivo. In this review, we focus on the recent advancements in engineered allosteric regulation and discuss the various bioengineered allosteric techniques available now, from chimeric GPCRs to chemogenetic and optogenetic switches. We highlight the benefits and pitfalls of each of these techniques as well as areas in which future improvements can be made. Additionally, we provide a brief discussion on implementation of engineered allosteric regulation approaches, demonstrating that these tools can shed light on elusive biological events and have the potential to be utilized in precision medicine.

α-Helix stabilization by co-operative side chain charge-reinforced interactions to phosphoserine in a basic kinase-substrate motif

How cellular functions are regulated through protein phosphorylation events that promote or inhibit protein–protein interactions (PPIs) is key to understanding regulatory molecular mechanisms. Whilst phosphorylation can orthosterically or allosterically influence protein recognition, phospho-driven changes in the conformation of recognition motifs are less well explored. We recently discovered that clathrin heavy chain recognizes phosphorylated TACC3 through a helical motif that, in the unphosphorylated protein, is disordered. However, it was unclear whether and how phosphorylation could stabilize a helix in a broader context. In the current manuscript, we address this challenge using poly-Ala-based model peptides and a suite of circular dichroism and nuclear magnetic resonance spectroscopies. We show that phosphorylation of a Ser residue stabilizes the α-helix in the context of an Arg_(i−3)pSer_i Lys_(i+4) triad through charge-reinforced side chain interactions with positive co-operativity, whilst phosphorylation of Thr induces an opposing response. This is significant as it may represent a general method for control of PPIs by phosphorylation; basic kinase-substrate motifs are common with 55 human protein kinases recognizing an Arg at a position −3 from the phosphorylated Ser, whilst the Arg_(i−3)Ser_i Lys_(i+4) is a motif found in over 2000 human proteins.

Peptide Design and Self-assembly into Targeted Nanostructure and Functional Materials

Peptides have been extensively utilized to construct nanomaterials that display targeted structure through hierarchical assembly. The self-assembly of both rationally designed peptides derived from naturally occurring domains in proteins as well as intuitively or computationally designed peptides that form β-sheets and helical secondary structures have been widely successful in constructing nanoscale morphologies with well-defined 1-d, 2-d, and 3-d architectures. In this review, we discuss these successes of peptide self-assembly, especially in the context of designing hierarchical materials. In particular, we emphasize the differences in the level of peptide design as an indicator of complexity within the targeted self-assembled materials and highlight future avenues for scientific and technological advances in this field.

Pharmacological Functionalization of Protein-Based Nanorobots as a Novel Tool for Drug Delivery in Cancer

The delivery of hydrophobic therapeutic agents to tumors is a challenge in the treatment of cancers. Here, we review recent advances in coiled-coil protein origami and discuss a proposed programmable protein origami structure, switchable by a protein kinase A/phosphatase switch, as an example of functionalization for designing future protein nanorobots.

A Brief History of De Novo Protein Design: Minimal, Rational, and Computational

Protein design has come of age, but how will it mature? In the 1980s and the 1990s, the primary motivation for de novo protein design was to test our understanding of the informational aspect of the protein-folding problem; i.e., how does protein sequence determine protein structure and function? This necessitated minimal and rational design approaches whereby the placement of each residue in a design was reasoned using chemical principles and/or biochemical knowledge. At that time, though with some notable exceptions, the use of computers to aid design was not widespread. Over the past two decades, the tables have turned and computational protein design is firmly established. Here, I illustrate this progress through a timeline of de novo protein structures that have been solved to atomic resolution and deposited in the Protein Data Bank. From this, it is clear that the impact of rational and computational design has been considerable: More-complex and more-sophisticated designs are being targeted with many being resolved to atomic resolution. Furthermore, our ability to generate and manipulate synthetic proteins has advanced to a point where they are providing realistic alternatives to natural protein functions for applications both in vitro and in cells. Also, and increasingly, computational protein design is becoming accessible to non-specialists. This all begs the questions: Is there still a place for minimal and rational design approaches? And, what challenges lie ahead for the burgeoning field of de novo protein design as a whole?

Expanding the versatility of natural and de novo designed coiled coils and helical bundles

Natural helical bundles (HBs) constitute a ubiquitous class of protein folds built of two or more longitudinally arranged α-helices. They adopt topologies that include symmetric, highly regular assemblies all the way to asymmetric, loosely packed domains. The diverse functional spectrum of HBs ranges from structural scaffolds to complex and dynamic effectors as molecular motors, signaling and sensing molecules, enzymes, and molecular switches. Symmetric HBs, particularly coiled coils, offer simple model systems providing an ideal entry point for protein folding and design studies. Herein, we review recent progress unveiling new structural features and functional mechanisms in natural HBs and cover staggering advances in the de novo design of HBs, giving rise to exotic structures and the creation of novel functions.

DE-STRESS: a user-friendly web application for the evaluation of protein designs

De novo protein design is a rapidly growing field, and there are now many interesting and useful examples of designed proteins in the literature. However, most designs could be classed as failures when characterised in the lab, usually as a result of low expression, misfolding, aggregation or lack of function. This high attrition rate makes protein design unreliable and costly. It is possible that some of these failures could be caught earlier in the design process if it were quick and easy to generate information and a set of high-quality metrics regarding designs, which could be used to make reproducible and data-driven decisions about which designs to characterise experimentally. We present DE-STRESS (DEsigned STRucture Evaluation ServiceS), a web application for evaluating structural models of designed and engineered proteins. DE-STRESS has been designed to be simple, intuitive to use and responsive. It provides a wealth of information regarding designs, as well as tools to help contextualise the results and formally describe the properties that a design requires to be fit for purpose.