Contact order¶
A normalized measure of how far apart along a protein sequence the residues forming native-state contacts tend to be.
Core Idea¶
Relative contact order averages sequence separation over declared native contacts and divides by chain length; contact definition, domain boundary and structural ensemble materially affect the value. A native structure supplies contacting residue pairs, their sequence separations are summed and normalized by contact count and protein length to express the locality of the fold topology. The abstraction is therefore identified by a declared carrier, a transformation or constraint over that carrier, and an invariant that tells an analyst whether the named structure is genuinely present.
Scope of Application¶
Contact order belongs to structural biology and is useful where the analyst can specify the typed structural biology carrier, including objects, relations, parameters, conventions, evidence, boundaries, and comparison targets, then evaluate the protein chain and length, native structure and ensemble, residue-index convention, contact-distance and sequence-separation thresholds, included contact pairs, normalization formula, uncertainty and any folding-rate comparison are explicit. The scope is broad within that domain but bounded by the need for the protein chain and length, native structure and ensemble, residue-index convention, contact-distance and sequence-separation thresholds, included contact pairs, normalization formula, uncertainty and any folding-rate comparison are explicit. Descriptive structural-biology metric only; no wet-lab, diagnostic, or intervention procedure is provided.
Clarity¶
The abstraction clarifies a crowded vocabulary by making the protein chain and length, native structure and ensemble, residue-index convention, contact-distance and sequence-separation thresholds, included contact pairs, normalization formula, uncertainty and any folding-rate comparison are explicit the center of the account. A claim should name the carrier, the governing operation or relation, the applicable assumptions, and the recognition test. A bare label is insufficient because the name Contact order can be used for a formal identity, an implementation, or a neighboring result unless carrier and convention are stated.
Manages Complexity¶
Without the abstraction, an analyst must reason directly over many local details: the carrier roles, admissibility assumptions, competing conventions, derived invariants, boundary cases, and proof or validation obligations specific to Contact order. Contact order compresses them into the roles in the structural signature. That compression permits comparison across instances without erasing the variables that determine validity. It also exposes which details may be varied safely and which are constitutive.
Abstract Reasoning¶
- Identify the carrier. State what the elements, states, objects, or observations are: the typed structural biology carrier, including objects, relations, parameters, conventions, evidence, boundaries, and comparison targets. Reject examples whose alleged carrier belongs to a different problem. 2. Lock the constitutive rule. Express the protein chain and length, native structure and ensemble, residue-index convention, contact-distance and sequence-separation thresholds, included contact pairs, normalization formula, uncertainty and any folding-rate comparison are explicit independently of one notation or implementation.
Knowledge Transfer¶
Knowledge transfers strongly among subfields of structural biology because they reuse the typed structural biology carrier, including objects, relations, parameters, conventions, evidence, boundaries, and comparison targets, A native structure supplies contacting residue pairs, their sequence separations are summed and normalized by contact count and protein length to express the locality of the fold topology., and type the carrier, state every parameter and convention in the definition, test that the protein chain and length, native structure and ensemble, residue-index convention, contact-distance and sequence-separation thresholds, included contact pairs, normalization formula, uncertainty and any folding-rate comparison are explicit, compare the nearest accepted identity, and report counterexamples, uncertainty, and limiting cases.
Relationships to Other Abstractions¶
Current abstraction Contact order Domain-specific
Parents (1) — more general patterns this builds on
-
Contact order is a kind of Metric Prime
The proposed strict upward parent is
prime:metric.
Hierarchy path (1) — routes to 1 parentless root
- Contact order → Metric → Function (Mapping)
Neighborhood in Abstraction Space¶
Contact order sits in a crowded region of the domain-specific corpus (33rd percentile for distinctiveness): several abstractions share nearly its structure, so a description that fits it tends to fit its neighbors too.
Family — Molecular Regulation & Cellular Information (23 abstractions)
Nearest neighbors
- Protein fragment library — 0.93
- Histone fold — 0.93
- Sequence feature variant type — 0.90
- Single-strand conformation polymorphism — 0.89
- Ka/Ks ratio — 0.89
Computed from structural-signature embeddings · 2026-09-08