TypeScript: @rtemis/a3

TypeScript implementation of the Amino Acid Annotation (A3) format — a structured JSON format for amino acid sequences with site, region, PTM, processing, and variant annotations.

Part of the rtemis-org/a3 monorepo.

Installation

npm install @rtemis/a3
# or
pnpm add @rtemis/a3

Quick Start

import { A3 } from "@rtemis/a3"

const a3 = new A3({
  sequence: "MKTAYIAKQR",
  annotations: {
    site: {
      "Active site": { index: [3, 5], type: "activeSite" },
    },
    region: {
      "Repeat 1": { index: [[1, 4]], type: "" },
    },
    ptm: {
      Phosphorylation: { index: [7], type: "" },
    },
    processing: {},
    variant: [{ position: 3, from: "K", to: "R" }],
  },
  metadata: {
    uniprot_id: "P12345",
    description: "Example protein",
    reference: "",
    organism: "Homo sapiens",
  },
})

a3.length         // 10
a3.residueAt(1)   // "M"
a3.toJSONString() // canonical JSON string

Parsing JSON

import { A3, A3ValidationError } from "@rtemis/a3"

try {
  const a3 = A3.fromJSONText(jsonString)
} catch (e) {
  if (e instanceof A3ValidationError) {
    console.error(e.issues) // Zod issue array with field paths
  }
}

File I/O (Node.js)

import { readJSON, writeJSON } from "@rtemis/a3"

const a3 = await readJSON("./protein.json")
await writeJSON(a3, "./output.json")

Wire Format

{
  "sequence": "MKTAYIAKQR",
  "annotations": {
    "site":       { "Active site": { "index": [3, 5],   "type": "activeSite" } },
    "region":     { "Repeat 1":    { "index": [[1, 4]], "type": "" } },
    "ptm":        { "Phospho":     { "index": [7],      "type": "" } },
    "processing": {},
    "variant":    [{ "position": 3, "from": "K", "to": "R" }]
  },
  "metadata": {
    "uniprot_id":  "P12345",
    "description": "Example protein",
    "reference":   "",
    "organism":    "Homo sapiens"
  }
}

All five annotation families are always present in output. Each annotation entry is { index, type } — bare arrays are rejected. Positions are 1-based, sorted, and deduplicated. Ranges are [start, end] pairs (start < end), sorted by start; overlapping ranges are rejected.

API

`new A3(input)` / `A3.fromData(input)`

Construct and validate. Throws A3ValidationError if input is invalid.

`A3.fromJSONText(text)`

Parse a JSON string and validate. Throws A3ParseError on invalid JSON, A3ValidationError on schema violations.

`a3.length`

Number of residues in the sequence.

`a3.residueAt(position)`

Return the residue at a 1-based position. Throws RangeError if out of bounds.

`a3.variantsAt(position)`

Return all variant records at a given 1-based position.

`a3.toData()`

Return the validated data object (frozen).

`a3.toJSONString(indent?)`

Serialize to a JSON string. Default indent is 2; pass 0 for compact output.

`JSON.stringify(a3)`

Works directly — toJSON() is implemented.

Exported Types

import type {
  A3Data,
  MetadataData,
  VariantData,
  SiteEntryData,
  RegionEntryData,
  FlexEntryData,
} from "@rtemis/a3"

License

MPL-2.0

TypeScript: @rtemis/a3

On this page