| 1. Domain | 1.1 Scope of the Domain | Boundaries | The range of phenomena the science includes and excludes. | Studies the three-dimensional structure, architecture, folding, assembly, and physical organization of biological macromolecules; excludes purely sequence-level biology without structural context or purely metabolic/kinetic analysis. |
| | Scale | The spatial, temporal, or organizational level at which the science operates (e.g., quantum, cellular, social, cosmic). | Operates from atomic and electronic scales (bonding, hydrogen bonding, side-chain interactions) to macromolecular structures (proteins, nucleic acids, complexes) and supramolecular assemblies (ribosomes, viral capsids). |
| 1.2 Ontological Commitments | Entities | The kinds of things assumed to exist within the domain (particles, organisms, agents, fields, etc.). | Amino acids, nucleotides, proteins, nucleic acids, motifs, domains, secondary/tertiary/quaternary structures, macromolecular complexes, water networks, ions, chaperones, folding intermediates. |
| | Properties | The fundamental attributes these entities possess (mass, charge, genotype, preference, etc.). | Charge distribution, hydrophobicity, stereochemistry, secondary-structure propensity, conformational stability, flexibility/rigidity, binding affinity, surface topology, molecular shape. |
| | Categories | The basic ontological types used to classify domain elements (substances, processes, relations, structures). | Structural motifs (α-helices, β-sheets, turns), domains, folds, nucleic-acid structural forms (A/B/Z-DNA, RNA motifs), macromolecular assemblies, intrinsically disordered regions, symmetry classes. |
| 1.3 State-Variables | Variables | The measurable or definable properties that describe system conditions. | Temperature, pH, ionic strength, redox state, ligand concentration, folding state, protonation state, conformational ensemble distribution, hydration shell organization, structural order/disorder. |
| | Parameterization | How variables encode and represent the system’s state. | States encoded via atomic coordinates, RMSD/Rg values, B-factors, hydrogen-bond counts, dihedral angles (φ/ψ/χ), folding free energy (ΔG_fold), structural alignment parameters, conformational ensembles. |
| 1.4 Admissible Idealizations | Simplifications | Conceptual reductions used to make the domain tractable (point masses, rational agents, perfect gases). | Treating macromolecules as static, rigid structures; using reduced representations (backbone only); ideal secondary structures; simplified solvent models; harmonic approximations; neglect of rare conformations. |
| | Validity Conditions | The limits and contexts in which idealizations hold or break down. | Valid for stable, well-folded proteins or nucleic acids; breaks down with intrinsically disordered regions, multistate folding landscapes, large conformational transitions, or strong solvent coupling. |
| 1.5 Domain Assumptions | Structural Assumptions | Background ontological stances such as determinism, continuity, randomness, discreteness. | 3D structure determines biological function; folding follows physicochemical rules; noncovalent interactions govern stability; water and ions strongly influence structure. |
| | Implicit Commitments | Unstated but necessary assumptions that shape the field’s conceptual structure. | Assumes meaningful mapping between structure and function, consistent steric/electronic behavior across residues/nucleotides, stable structural ensembles, and transferable folding/packing principles. |
| 1.6 Internal Coherence Requirements | Consistency | The demand that domain concepts do not contradict one another. | Requires coherence among atomic coordinates, experimental structural data, thermodynamic stability, folding models, and functional evidence without contradiction. |
| | Compatibility | The requirement that entities, variables, and assumptions fit together into a unified descriptive framework. | Demands alignment between structural models, spectroscopic/crystallographic data, molecular-dynamics simulations, evolutionary constraints, and biophysical measurements within a unified framework. |
| 2. Evidence Layer | 2.1 Observable Phenomena | Observables | The aspects of the domain that can produce detectable signals accessible to measurement. | X-ray diffraction patterns, NMR chemical shifts/NOEs/RDCs, cryo-EM density maps, circular dichroism spectra, fluorescence quenching, FRET signals, hydrogen-exchange rates, SAXS profiles, unfolding/refolding curves. |
| | Detection Limits | The boundaries of what can be resolved or sensed by current instruments or methods. | Limited by resolution (Å), signal-to-noise, sample concentration, molecular size, flexibility, disorder, radiation damage, crystallization difficulty, labeling efficiency, and background scattering. |
| 2.2 Measurement Systems | Units | Standardized quantifications (meters, seconds, volts, decibels, dollars, etc.) necessary for consistent comparison. | Distance (Å), chemical shift (ppm), electron density (a.u.), scattering intensity (a.u.), wavelength (nm), temperature (°C/K), pH units, fluorescence intensity, FRET efficiencies, time (ms–min). |
| | Instruments | Devices and tools (microscopes, spectrometers, sensors, surveys, detectors) used to produce measurements. | X-ray diffractometers, cryo-EM microscopes, NMR spectrometers, CD spectrometers, fluorescence spectrometers, SAXS beamlines, HDX-MS systems, AFM, smFRET setups, molecular-imaging systems, computational MD. |
| 2.3 Operational Definitions | Definitions | Terms defined by specific measurement procedures, ensuring empirical clarity. | Secondary structure via CD signatures; atomic coordinates defined by crystallography/EM/NMR; hydrogen bonds by geometric criteria; folding/unfolding defined by transition midpoint; disorder defined via B-factor/RMSF. |
| | Procedures | The explicit steps required to perform a measurement in a reproducible way. | Crystallization, vitrification, isotopic labeling, pulse sequences, diffraction data collection, map reconstruction, MD ensemble generation, hydrogen–deuterium exchange workflows, thermal-ramp unfolding assays. |
| 2.4 Data Acquisition | Protocols | Formal processes for gathering data under controlled or standardized conditions. | Multi-angle diffraction, multi-frame cryo-EM imaging, NMR multidimensional experiments, SAXS scattering curves, time-resolved fluorescence/FRET acquisition, HDX sampling intervals, titration-dependent structural scans. |
| | Sampling | Rules determining which subset of the domain is measured and how representative it is. | Replicate crystals/EM grids, multiple NMR timepoints, ensemble-size sampling for MD, replicate SAXS measurements, multi-frame alignment, per-residue HDX sampling, random grid selection for EM micrographs. |
| 2.5 Data Character & Format | Data Types | The form raw evidence takes (time series, spectra, images, counts, qualitative records). | PDB coordinate files, EM density maps, NMR restraints, CD spectra, SAXS curves, HDX-MS deuterium uptake profiles, fluorescence/FRET time series, RMSD/RMSF datasets, hydrogen-bond networks, thermodynamic unfolding curves. |
| | Resolution | The granularity or precision with which data is captured. | Determined by diffraction limit (Å), EM particle count and alignment accuracy, NMR signal dispersion, labeling efficiency, detector sensitivity, scattering power, acquisition time, and sample homogeneity. |
| 2.6 Reliability & Calibration | Calibration | Adjustment procedures ensuring instruments produce accurate results. | Wavelength calibration (X-ray), magnetic-field calibration (NMR), detector gain, cryo-EM contrast-transfer calibration, SAXS intensity scaling, temperature/pH calibration, mass calibration in HDX-MS, reference standards. |
| | Error Characterization | Identification and quantification of noise, uncertainty, bias, and measurement error. | Identifying noise, radiation damage, motion blur, sample heterogeneity, misfolded states, peak overlap, incorrect assignments, reconstruction artifacts, baseline drift, and statistical uncertainty across ensembles. |
| 3. Structural Layer | 3.1 Patterns & Regularities | Laws / Relations | Stable, repeatable patterns governing how observables behave across conditions. | Folding rules, hydrophobic-core formation, secondary-structure stabilization laws (H-bonding patterns), symmetry in macromolecular assemblies, sequence–structure correlations, packing regularities, nucleic-acid base-pairing rules. |
| | Invariants | Quantities or properties that remain constant under transformations (symmetries, conservation laws). | Conserved motifs (helix-turn-helix, β-hairpins, Rossmann folds), invariant catalytic cores across homologous proteins, conserved domain architectures, canonical base-pair geometries, stereochemical constraints of backbone dihedrals. |
| 3.2 Causal Architecture | Mechanisms | Underlying processes or structures that produce the observed regularities. | Folding mechanisms (two-state, multi-state), domain assembly, hydrogen bonding, hydrophobic collapse, ionic/metal coordination, pi-stacking, chaperone-assisted folding, conformational switching, cooperative interactions. |
| | Pathways | Organized sequences of interactions forming a causal chain or network. | Folding pathways, assembly of complexes, allosteric transitions, helix/strand propagation, loop closure, RNA folding cascades, misfolding → aggregation pathways (amyloidogenesis). |
| 3.3 Theoretical Vocabulary | Concepts | Core terms that encode the domain’s structure (force, gene, equilibrium, field). | Secondary/tertiary/quaternary structure, motifs/domains, folds, hydrophobic core, salt bridges, disulfide bonds, conformational ensemble, allostery, cooperativity, energy landscape, free-energy funnel, RMSD/Rg. |
| | Classifications | Taxonomies, categories, or typologies that organize entities and relations. | Protein fold families, domain architectures, RNA/DNA secondary-structure classes, symmetry classes in complexes, intrinsically disordered proteins (IDPs), structured vs unstructured regions. |
| 3.4 Formal Representations | Equations | Mathematical constructs expressing laws, relations, or mechanisms. | Folding free-energy equations (ΔG_fold), Boltzmann population formulas, hydrogen-bond geometry equations, Ramachandran constraints, radius-of-gyration formulas, cooperativity equations, two-state kinetic equations. |
| | Models | Structured representations—mathematical, computational, or conceptual—used to predict and explain phenomena. | Energy-landscape models, molecular-dynamics models, statistical coil models, homology modeling, coarse-grained structural models, elastic network models, Markov-state folding models. |
| 3.5 Idealized Structures | Simplified Models | Purposeful abstractions that capture essential dynamics while omitting irrelevant detail. | Perfect helices/sheets, rigid domains, static conformers, neglect of solvent, no dynamic fluctuations, purely harmonic potentials, two-state folding, ideal cooperative transitions. |
| | Limit Conditions | Regimes where specific models or approximations hold (classical vs. quantum, linear vs. nonlinear). | Break down with IDPs, large conformational heterogeneity, multi-domain flexibility, solvent-coupled folding, crowding effects, post-translational modifications, metal–ion dependency, and multi-state energy surfaces. |
| 3.6 Integrative Frameworks | Unifying Theories | Higher-order structures that connect disparate laws or mechanisms under a coherent whole. | Integration of structure, thermodynamics, kinetics, and function into a single model; coupling structural data with evolutionary constraints; unified protein/RNA folding landscapes; multi-scale structural frameworks linking atoms → motifs → complexes → cellular assemblies. |
| | Interdisciplinary Links | Points where the theory connects to adjacent sciences or larger explanatory systems. | Connects to molecular biology, biophysics, structural genomics, computational biology, medicinal chemistry, systems biology, and nanotechnology (biomolecular materials, scaffolds). |
| 4. Method Layer | 4.1 Inquiry Design | Experimental Design | Structured plans for manipulating variables to test causal claims. | Controlling temperature, pH, ionic strength, ligand concentration, isotopic labeling, crystallization/vitrification conditions, NMR pulse schemes, and EM imaging parameters to test structural hypotheses and folding/assembly behavior. |
| | Observational Design | Systematic approaches for gathering non-manipulated data (surveys, field studies, natural experiments). | Monitoring spontaneous folding/unfolding, conformational drift, thermal fluctuations, disorder emergence, ligand-free structural dynamics, hydration changes, and native-state behavior without imposed perturbation. |
| 4.2 Testing & Validation | Hypothesis Testing | Procedures for evaluating whether evidence supports or contradicts specific claims. | Comparing predicted secondary/tertiary structures, motif/domain boundaries, stabilizing interactions, conformational changes, and allosteric mechanisms with data from XRD, cryo-EM, NMR, SAXS, HDX-MS, and MD simulations. |
| | Replication | The requirement that results be independently reproducible under similar conditions. | Repeating crystallization trials, EM grid preparations, NMR experiments, SAXS measurements, HDX timepoints, fluorescence/FRET runs, MD replicates, and structural alignments to ensure reproducibility across independent experiments. |
| 4.3 Inference & Evaluation | Statistical Inference | Rules for drawing conclusions from noisy or incomplete data. | Assessing confidence in atomic coordinates, RMSD/RMSF values, B-factor distributions, ensemble variability, hydrogen-exchange rates, spectral peak assignments, model vs map correlations, and thermodynamic folding parameters. |
| | Model Comparison | Criteria (fit, simplicity, predictive accuracy, robustness) used to evaluate competing models. | Evaluating structural models from XRD vs EM vs NMR, comparing MD-derived ensembles to experimental data, testing secondary-structure predictions, comparing energy landscapes, and ranking alternative conformational hypotheses. |
| 4.4 Error Management | Error Analysis | Identification and quantification of random and systematic errors. | Identifying noise, radiation damage, sample heterogeneity, misfolded species, crystallographic artifacts, EM reconstruction errors, NMR peak overlap/misassignment, SAXS baseline issues, HDX back-exchange, and simulation artifacts. |
| | Bias Control | Methods for minimizing subjective, instrumental, or procedural biases. | Blinding structural interpretation when possible, validating models against multiple experimental methods, using orthogonal datasets, avoiding overfitting density/noise, standardizing sample prep, and ensuring correct labeling. |
| 4.5 Adjudication & Revision | Peer Scrutiny | Collective evaluation of claims through critique, review, and debate. | Independent review of structural models, refinement strategies, peak assignments, MD sampling depth, EM reconstruction parameters, crystallographic indexing, SAXS fits, and claims of novel folds or mechanisms. |
| | Theory Revision | Procedures for modifying, replacing, or discarding models based on new evidence. | Updating folding models, reassigning domain boundaries, revising interaction networks, adjusting energy landscapes, correcting erroneous coordinates, and integrating new data that contradicts earlier structural interpretations. |
| 4.6 Integrity Conditions | Transparency | Requirements to disclose methods, data, assumptions, and limitations. | Full reporting of sample preparation, crystallization/EM/NMR/SAXS conditions, data-processing pipelines, refinement parameters, MD protocols, error estimates, structural uncertainties, and validation metrics (e.g., R-free, FSC, restraint violations). |
| | Ethical Standards | Norms ensuring responsible conduct in experimentation, data handling, and publication. | Honest reporting of ambiguous density, disordered regions, failed crystals, low-resolution data, uncertain assignments, simulation limitations, and adherence to structural-data deposition and reproducibility standards. |