01Establish which signals belong to which atoms

A spectrum contains resonances, but a structural explanation needs assignments: connections between those resonances and specified nuclei. Without that connection, a signal at a particular chemical shift cannot simply be labelled as evidence about a chosen residue.

Baskaran and colleagues describe the structural-NMR workflow as combining signal assignments with experimental restraints and calculated coordinates. Through-bond experiments help establish assignments; through-space measurements can supply information about spatial proximity. These are different relationships and should not be collapsed into a single idea of connection.Baskaran and colleagues — Restraint validation of biomolecular NMR structures (opens in a new tab)

For example, two residues far apart in the written sequence may approach each other in a folded conformation. Evidence of proximity does not move them next to one another in the sequence or establish a new covalent bond.

02Follow the step from measurements to geometry

In a primary study of neuropeptide Y residues 13–36, Labelle and colleagues used several two-dimensional proton-NMR experiments to assign signals. Their NOESY measurements supplied intraresidue and interresidue distance ranges, which were used in molecular modelling. The reported structure described the peptide under the solution conditions examined.Labelle and colleagues — Solution structure of neuropeptide Y 13–36 (opens in a new tab)

The important distinction is between a distance range and a perfectly known distance. A model may satisfy a measured bound in several ways, particularly where fewer independent observations constrain the chain. Additional experimental information can narrow the possibilities without turning every atom into an exactly located point.

Imagine an original geometric analogy: three known distances may locate a point more tightly than one distance alone. A single distance allows many positions. In a peptide the constraints are more complex, but the same reasoning explains why the distribution of supporting observations matters alongside their total number.

03Interpret a collection of models carefully

NMR structures are often displayed as multiple superimposed models. Their spread should not automatically be read as a time-lapse movie or as the measured population of each conformation. The models are selected products of a calculation and its restraints.

Consider a figure with a closely aligned middle section and widely separated ends. The drawing makes the contrast visible, but its explanation still requires the experimental record. Sparse restraints, molecular flexibility and modelling choices are not interchangeable conclusions.

The Protein Data Bank validation work evaluates agreement between deposited structures and distance or dihedral-angle restraints. This makes it possible to inspect restraint violations rather than relying only on a visually attractive fold. Chemical geometry and agreement with experimental restraints are complementary checks.Baskaran and colleagues — Restraint validation of biomolecular NMR structures (opens in a new tab)

A model can look chemically tidy while fitting observations poorly. Conversely, checking only the fit can miss implausible geometry. Neither check should be replaced by the visual smoothness of a ribbon diagram.

04Keep the claim tied to the measured system

A useful structure record identifies the peptide form, solution conditions, assignments, experimental restraints, calculation and validation. This allows a reader to distinguish a detailed investigation from the bare statement that NMR was performed.

A published structure of a named peptide does not establish that a different vial contains that same material. Equally, a structural experiment is not automatically an amount assay. Those are separate questions requiring evidence linked to the actual sample.