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Dynamic Protein Structure Paradox: An Integrative Framework for Endpoint-Conditioned Evidentiary Sufficiency in Structure-to-Function Claims.

Accurate coordinates for a represented protein state do not, by themselves, establish activity or any other condition-specific function. This article defines the Dynamic Protein Structure Paradox (DPSP) as the apparent conflict between structural accuracy and functional underdetermination and develops it as an integrative evidentiary assessment framework rather than a new theory or paradigm. The underlying problem has been longstanding, since structural genomics, function annotation, allostery, and disorder research each established that fold does not determine function and that function does not determine fold. DPSP consolidates those results into one endpoint-conditioned rule. Once a measurable endpoint is defined, it assesses four coupled dimensions: relevant-state completeness, context completeness, ensemble or kinetic dependence, and chemical dependence. A rubric rates each dimension as adequate, uncertain, or missing, and a materiality test determines which gaps influence the stated decision. The outcome is one of three mutually exclusive modes of utilization: geometry-led, conditional, or function-measured. The deliverable is a concise evidence statement delineating what the structure supports, which decisive variable remains unmeasured, and what corroboration is necessary. DPSP complements, rather than replaces, existing structural, ensemble, and computational approaches. The framework remains unvalidated, its thresholds are provisional, and the studies necessary to confirm or refute it are specified.

Proteins

Hidden genomic structure and widespread structural polymorphism across environmental gradients in the spiny sea star Marthasterias glacialis.

Genomic regions of reduced recombination can preserve linkage among co-adapted alleles, facilitating local adaptation despite high connectivity. Such regions-often generated by chromosomal inversions-may be especially important in highly dispersive marine taxa yet remain poorly documented in echinoderms. Here, we combined a chromosome-level reference genome with genome-wide ddRAD-seq from 296 Marthasterias glacialis individuals across 19 Atlantic-Mediterranean locations to quantify population structure and scan for recombination-suppressed haploblocks. Genome-wide neutral markers showed significant population differentiation together with evidence of high connectivity, revealed by the presence of inter-ecoregion migrants. Additionally, we identified 16 polymorphic haploblocks with patterns consistent with putative chromosomal inversions spanning 18.6% of the genome. Haploblock haplotypes were strongly environmentally and geographically structured and contained genes with key functions in stress response, osmoregulation and thermal tolerance. Haplotype distributions also paralleled previously described mitochondrial lineages despite nuclear gene flow, consistent with a model of ancient divergence followed by secondary contact. Overall, our results suggest a role for widespread structural polymorphism in adaptive differentiation in Echinodermata, providing a framework for linking echinoderm genome rearrangements to ecological divergence. Marthasterias glacialis thus emerges as a promising system to explore how structural variation contributes to adaptation and genome evolution in highly dispersive organisms.

Animals

Differences in structural color and population genetic structure of Western and Central Palearctic Polyommatus icarus populations.

The blue structural coloration of male Polyommatus icarus butterflies functions as a sexual signaling trait and exhibits remarkable spectral stability within populations despite being generated by highly complex photonic nanoarchitectures. The correlation of the blue sexual signaling color and population genetic variation of the butterflies was investigated across the Western and Central Palearctic regions. Dorsal wing reflectance spectra was measured for 95 male specimens and compared with the population genetic structure revealed in 99 specimens by 18 recently developed microsatellites. Reflectance measurements indicated a clear separation between the European and Central Asian populations, consistent with our previous findings, while the intermediate populations near the Ural Mountains exhibited distinct European spectral characteristics. In contrast, genetic variation showed limited structuring and correlated primarily with geographic distance, as indicated by a significant isolation-by-distance pattern. Thus, although both reflectance and genetic variations are geographically structured, spectral properties are only weakly correlated with genetic differentiation. Populations near the Ural Mountains exhibited genetic ancestry linked to Central Palearctic groups, while displaying distinct Western Palearctic coloration, suggesting that the focal species' sexual signaling is strongly influenced by local factors. These findings suggest that sexual signaling coloration may evolve at least partially independently of the neutral genetic background, offering additional insight into evolutionary divergence across broad geographic scales.

Animals

[Structure and configuration of human tendons. II. Development of tendon structure during ontogenesis].

In infants born in the 24th--30th weeks of the gravidity the praenatal development and the process of the organization of the tendinous structure have been examined by the authors. By means of photo- and polarization microscopic examinations it was found that the tendon of the flexor hand muscles (M. flexor carpi radialis, M. flexor digitorum comm.) shows mature tendinous structure earlier, than the tendons of the flexor muscles of the lower extremity (M. semitendinosus femoris, M. triceps surae). The tendons of the extensor muscles of the lower extremity (M. quadriceps femoris, M. tibialis ant.) are underdeveloped and inordinate in the foetal life--their structure develops only during the postnatal life.

Hand

Intertypic Recombination Between Coxsackievirus A16 and Enterovirus A71 Structural and Non-Structural Genes Modulates Virulence and Protection Efficacy.

Background/Objectives: Enterovirus A71 (EV-A71) and coxsackievirus A16 (CVA16) are major causative agents of hand, foot and mouth disease (HFMD), often co-circulating and occasionally undergoing genetic recombination. While natural recombinants often involve genomic regions encoding non-structural proteins, their effects on replication and pathogenesis remain unclear. Methods: To address this, four chimera viruses (Chi-CCE, Chi-ECE, Chi-EEC, and Chi-CEC) were constructed with 5'UTR, capsid P1, and non-structural P2 and P3 genes, from CVA16 (denoted as C) or EV-A71 (denoted as E). These chimeras were tested for replication kinetics and cytopathic effects in rhabdomyosarcoma cells while in vivo virulence and protection efficacy were evaluated using a newborn BALB/c mouse model. Results: All chimeric viruses remained viable and exhibited higher replication than CVA16. In vivo, all chimeric viruses were avirulent except Chi-CCE and CVA16, which showed high virulence and viral titres in the brains and limbs of infected newborn mice. This suggests that 5'UTR and capsid P1 genes of CVA16 are critical genetic determinants of virulence. Notably, only the anti-inflammatory cytokine IL-10 was elevated, suggesting potential immune modulation during infection. Inactivated Chi-CCE immunisation conferred 100% protection against lethal CVA16 or mouse-adapted EV-A71 challenge revealing its potential as a bivalent vaccine candidate. Conclusions: Our study demonstrates that recombination between CVA16 and EV-A71 influences viral virulence and protection efficacy with implications for future development of multivalent vaccines.

coxsackievirus A16

Application of the Free-Wilson technique to structurally related series of homologues. Quantitative structure-activity relationship studies of narcotic analgetics.

A series of benzomorphans with ED50 values determined in vivo by the hot-plate method in mice is analyzed by the modified Free-Wilson method. The QSAR yields 36 substituent constants (ai) with contributions to the overall activity in agreement with experimental data. Substituent constant values obtained for benzomorphans are used in calculating log (1/C) values for six morphinans. An excellent correlation is obtained (r = 0.95) between the six calculated and observed activities. The possibility of extending the Free-Wilson approach from one series of homologues to another is demonstrated.

Analgesics, Opioid

Structure-basicity and structure-affinity relationships of beta-adrenergic blocking agents.

pKa's of fourteen beta-receptor blockers, isoproterenol and norepinephrine, were determined potentiometrically. A Hammett analysis indicated that the influence of ring substituents on the basicity of the amines is attenuated by the ethanolic chain and abolished by the propranoloxy chain of beta-receptor blockers. The effect of ring substituents in phenoxypropranolamines upon affinity for the beta-adrengeric receptors is therefore unrelated to the strength of the bases. Two alterantive hypotheses are fowarded to explain why phenoxypropranolamines have greater affinities for the beta-receptors than phenethanolamines.

Adrenergic beta-Antagonists

Iodination-deiodination. A radiochemical method for detection of structure and changes in structure in RNA.

Bound iodine is released from radioiodinated nucleotides in polymers exposed to sodium bisulfite. The rate of bisulfite-catalyzed deiodination of pyrimidines can be controlled both by change of temperature of pH and is also dependent on the molecular association of the nucleotide. The rate of release of iodine from iodocytidine in polycytidylate is greater than the rate of elimination from RNA. Experiments testing the influence of base-pairing of the iodopyrimidines in synthetic polynucleotides showed that pairing of the substituted nucleotide protected the iodine bond. The rates of bisulfite-catalyzed deiodination of several radioiodinated RNAs were measured. The action of bisulfite on all single stranded RNAs tested was multiphasic consisting of a rapid early deiodination reaction supplanted by a slower phase which was followed by reacceleration of release. The release of iodine from double stranded RNA and DNA-RNA duplexes was retarded in comparison with the release from ribosomal and messenger RNA fractions. The deiodination profiles of single and double stranded RNA suggested that the intermediate stage iodine release is governed by melting of paired zones of low stability. Late release may result from destablization of the molecule through the addition of bisulfite to the pyrimidine ring or deamination. The effect of several substances expected to complex with polynucleotides was tested. Acridine orange and ethidium bromide increased loss of iodine from ribosomal RNA but slightly decreased elimination from double stranded viral RNA. A basic protein fraction isolated from ribosomal particles accelerated the deiodination of ribosomal RNA. While the destabilization caused by this protein fraction was greater than that caused by an equal amount of albumin, as tested the effect was non-specific. The results show that a change in sensitivity to chemical deiodination may folow the interaction of small amounts of protein with polynucleotides.

Animals

Newly Developed Structure-Based Methods Do Not Outperform Standard Sequence-Based Methods for Large-Scale Phylogenomics.

Recent developments in protein structure prediction have allowed the use of this previously limited source of information at genome-wide scales. It has been proposed that the use of structural information may offer advantages over sequences in phylogenetic reconstruction, due to their slower rate of evolution and direct correlation to function. Here, we examined how recently developed methods for structure-based homology search and tree reconstruction compare with current state-of-the-art sequence-based methods in reconstructing genome-wide collections of gene phylogenies (i.e. phylomes). While structure-based methods can be useful in specific scenarios, we found that their current performance does not justify using the newly developed structure-based methods as a default choice in large-scale phylogenetic studies. On the one hand, the best performing sequence-based tree reconstruction methods still outperform structure-based methods for this task. On the other hand, structure-based homology detection methods provide larger lists of candidate homologs, as previously reported. However, this comes at the expense of missing hits identified by sequence-based methods, as well as providing sets of homolog candidates with higher fractions of false positives. These insights help to guide the use of structural data in comparative genomics and highlight the need to continue improving structure-based approaches. Our pipeline is fully reproducible and has been implemented in a Snakemake workflow. This will facilitate a continuous assessment of future improvements of structure-based tools in the AlphaFold era.

Phylogeny

Structural genomics sheds light on protein functions and remote homologs across the insect tree of life.

Protein structure bridges the sequence-function relationship, enabling deep exploration of biological processes across diverse organisms. Insects, the most diverse animal lineage, accounting for over 50% of all described animal species, provide an exceptional system for exploring sequence-structure-function relationships. Here, we reconstructed a comprehensive and well-resolved phylogeny of 4854 insects, spanning all orders. Leveraging this framework, we created an atlas of 13.29 million predicted protein structures from 824 representative species, including 11.63 million newly predicted structures. Structural clustering revealed that proteins with divergent sequences but similar structures could be effectively grouped together. Structural similarity searches against proteins with well-characterized functions yielded annotations for 7.61 million insect proteins, including up to 14% of previously unannotated proteins. We further identified 750 million remote homologs between insect proteins, many of which trace back to ancient branches of the insect phylogeny. Remarkably, despite extensive sequence divergence, cGAS-like receptors (cGLRs) were structurally conserved across all 824 insects. Experimental assays demonstrated that these structurally identified cGLRs play a crucial role in antiviral defense in the yellow fever mosquito. Our findings highlight the significance of structural genomics for understanding protein function and evolution across the tree of life.

Animals

PMGen: from peptide-MHC structure prediction to peptide generation.

MOTIVATION: Accurate structural modeling of peptide-major histocompatibility complex (pMHC) complexes is essential for structure-driven immunotherapy design, yet current prediction tools suffer from narrow class coverage, restricted peptide lengths, insufficient accuracy, and a lack of built-in structure-aware peptide sampling. Consequently, most mimotope and altered peptide ligand designs rely solely on sequence substitution, leaving spatial and biophysical insights from pMHC structures largely unexploited. RESULTS: We introduce peptide-MHC generator (PMGen), an integrated framework for structure prediction and structure-guided design of variable-length peptides across MHC Class I and II. PMGen enforces anchor constraints within AlphaFold2 through two complementary strategies, initial guess and template engineering, achieving state-of-the-art structural fidelity without model fine-tuning. On a comprehensive benchmark, PMGen outperforms all existing methods, yielding median peptide-core Cα RMSDs of 0.62 Å for MHC-I and 0.33 Å for MHC-II. We show that PMGen can recover incorrectly predicted anchor positions and that AlphaFold pLDDT scores enable sequence-independent binding-core identification. Applied to a published neoantigen/wild-type pair, PMGen accurately captures mutation-induced conformational changes. Beyond structure prediction, we show that ProteinMPNN sampling on PMGen-predicted backbones yields higher affinity peptides while preserving the parental 3D conformation. Using PMGen to generate 63 817 high-confidence pMHC structures as training data, we further improve ProteinMPNN's peptide sequence recovery from 0.14 to 0.64 on a test set of 85 unseen MHC-I alleles, highlighting the value of accurate predicted structures for downstream machine learning tasks. AVAILABILITY AND IMPLEMENTATION: PMGen is freely available at https://github.com/soedinglab/PMGen, with an interactive Colab notebook at https://colab.research.google.com/github/soedinglab/PMGen/blob/master/colab.ipynb.

Peptides

Balancing under constraint: Structural insights into norovirus evolution and antigenic innovation.

Norovirus is the leading cause of acute viral gastroenteritis worldwide. While genomic studies have revealed its diversity and evolutionary patterns, the structural mechanisms driving viral adaptation remain poorly understood. Here, we establish a comprehensive structural database of norovirus VP1 P-domains across nine genogroups (GI-GIX) through large-scale AlphaFold2 predictions. By integrating phylogenetic analysis of VP1 sequences and structures, we demonstrate that sequence and structural evolution show overall concordance under purifying selection, yet significant local discrepancies reveal distinct patterns of convergent evolution shaped by structural constraints and functional divergence. Focusing on the predominant GII.4 genotype, we found that compared to near-full-genome and nucleotide trees, only the VP1 amino acid tree reliably clustered GII.4 variants in chronological order as monophyletic groups. We further identify a hierarchical evolutionary strategy: positive selection may drive structural hypervariability in major antigenic epitopes D and C for immune escape, with epitope D exhibiting pronounced structural flexibility that complicates its structural characterization, whereas coevolutionary analysis uncovers a broad network of compensatory interactions spanning multiple epitopes, with striking enrichment in epitope A. These epitopes exhibited a pattern of "sequence plasticity with structural conservation", maintained by coevolutionary constraints that preserve conformational integrity. Together, these findings suggest that norovirus vaccine strategies targeting the structurally conserved conformations of epitopes A and G could overcome the limitations of traditional strain-specific approaches, offering a pathway toward broad protection against evolving viral diversity.

Norovirus

3D Proteomics: Structural, Functional, Chemical and Biomarker Discovery Proteomics With LiP-MS.

Protein structural dynamics drive changes in protein function, making the capture of such dynamics essential for interrogating biological systems. Here we review limited proteolysis coupled to mass spectrometry (LiP-MS), a structural and chemical proteomics method that uses changes in susceptibility to protease cleavage to profile proteome-wide protein structural changes within complex biological samples. In the decade since its development, LiP-MS has become a broadly used structural proteomics method, with peptide-level resolution. It has identified drug targets, delineated altered cellular pathways in response to complex perturbations, revealed structural information on otherwise challenging protein targets, and demonstrated the new concept of structural biomarkers of disease. Because LiP-MS simultaneously probes numerous types of molecular events, such as molecular binding, changes in enzyme activity, chemical modifications, allosteric conformational changes, aggregation, and unfolding, it supports a new proteomics workflow which we term 3D proteomics. This workflow enables the detection of specific functional sites within proteins that are altered upon perturbation, thereby guiding the generation of molecular hypotheses. Further, by globally profiling structural in addition to protein abundance changes, LiP-MS has proven able to greatly increase the information content of functional proteomics screens. In sum, LiP-MS has supported the development of a novel conceptual framework for generating, visualizing, and interpreting structural proteomics data with peptide level resolution, thereby comprehensively probing biological systems. Here we survey the applications of LiP-MS, discuss methodological variants developed by us and others, and describe the use of this new type of omics readout for structural, functional, chemical, and biomarker discovery proteomics.

Proteomics

Inference of Cytochrome P450 Evolutionary History Using Structural and Physicochemical Metrics.

Cytochrome P450s are a superfamily of heme-binding monooxygenases involved with the detoxification of intrinsic and extrinsic toxins. They are near ubiquitous within biological domains and are found in all domains. Members of families within the superfamily are defined based on amino acid identity thresholds, with thresholds as low as 40% in some families. Relationships among Cytochrome P450 families have proven elusive due to sub-Twilight Zone interfamily identities (<30%) that result in poor multiple sequence alignment quality and thus low levels of support for downstream phylogenetic reconstructions. Despite the low identities, Cytochrome P450 structures are remarkably well conserved both within and among families. In such cases, structural phylogenetics has the potential to unveil elusive relationships because the selectively favored physicochemical properties giving rise to the structure and function of the proteins persist despite sequence-level divergence. Recently, in two separate publications, we demonstrated that by utilizing physicochemical vectors, dynamic time warping, and hierarchical clustering (PCDTW), large swaths of protein domain families and betacoronavirus receptor-binding domain clades were congruent with validated functional/structural relationships. These were important findings because anomalous sequence alignment-based maximum likelihood phylogenetic findings, which were not congruent with the known functional relationships, were resolved. That also validated the use of physicochemical vectors in making inferences about structural/functional homology. Additionally, it illuminated that the same methods might be applied to other protein families with relationships that are difficult to resolve from sequence data alone. Herein, we used Molecular Weight and Hydrophobicity Physicochemical Dynamic Time Warping (MWHP PCDTW) along with structural and sequence alignment-based phylogenetic methodologies to analyze all of the Cytochrome P450s found both in the high-fidelity Structural Classificaction of Proteins (SCOP) database and the reviewed sequences with both experimentally resolved and de novo predicted structures in the Protein Data Bank and the AlphaFold (AF) Protein Structure Database, respectively. We compared the resulting phylogenetic topologies and found that in some cases, structure-based methods may be less able to resolve random/convergent similarity than physicochemical and sequence-based methodologies. This finding agrees with previous findings that demonstrate the usefulness of physicochemical properties in resolving both random structural similarity and potentially convergent relationships.

Cytochrome P-450 Enzyme System

A structural bridge between dengue virus tandem xrRNAs facilitates coordination of exonuclease resistance.

Orthoflavivirus RNA genomes resist host 5'-3' exoribonucleases to produce subgenomic flaviviral RNAs (sfRNAs). This resistance is conferred by exoribonuclease-resistant RNA (xrRNA) structures within the viral 3' untranslated region that often occur in tandem, and whose function can be coupled. In dengue virus serotype 2 (DENV2), this coupling results in changing patterns of sfRNA identity and abundance associated with the ability of the virus to adapt to host vs. vector infections. The physical basis of this coupling was unknown. Using a combination of virology, biochemistry, bioinformatics, structural biology, and biophysics, we explored the structural and sequence determinants of tandem xrRNA coupling in DENV2. We discovered that the spatial proximity, order, and structural integrity of the tandem xrRNAs are all important for coupling. Furthermore, an unpaired A-rich linker that lies between the two xrRNAs is essential in stabilizing a specific structure that correlates to coupling. This A-rich sequence likely forms tertiary contacts with an adjacent stem-loop structure to form a physical bridge between the two xrRNAs, a finding that is supported by a mid-resolution cryo-electron microscopy (cryo-EM) map of the DENV2 tandem xrRNAs. Disruption of the structure of this bridge by mutation changes the relative orientation or spacing between the tandem xrRNAs, which is correlated to their functional coupling. These findings help provide an explanation for the coupling between tandem xrRNAs, suggesting a new mechanistic hypothesis in which the two tandem xrRNAs can simultaneously encounter Xrn1.IMPORTANCEDengue virus (DENV) generates non-coding subgenomic flaviviral RNAs (sfRNAs) that affect several cellular pathways and are important for successful infection. These sfRNAs are formed by structured RNA elements in the viral genome called exoribonuclease-resistant RNAs (xrRNAs), which fold into a distinct three-dimensional topology to block degradation by host cell exoribonucleases and often occur in tandem. Specific patterns of sfRNAs made during infection are important for host vs. vector fitness, and in DENV2, this pattern depends on functional coupling between tandem xrRNAs. However, the source of this functional coupling was unknown. We determined that an unpaired A-rich linker between the tandem xrRNAs is necessary for creating a structural bridge between the tandem xrRNAs. This bridge appears to favor a specific orientation between the tandem xrRNAs that is correlated to coupling and therefore to the patterns and relative abundance of sfRNAs produced during infection.

Dengue Virus