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Protein science is the study of protein structure, function, design and applications. The Protein Society describes the field this way, and it extends to the roles proteins play in cell biology, genetics and evolution. This page maps the field, explains the four levels of protein structure, and points to the CASRAI method guides for specific tools.
Short answer
Protein science asks how a protein’s amino acid sequence determines its three-dimensional shape, how that shape produces function, and how the knowledge can be used, for example to design new proteins. Researchers and lab staff meet it whenever they express, purify, characterise or model a protein.
Definition and scope
The Protein Society, the professional society behind the journal Protein Science, frames the field as covering protein structure, function, design and applications (Protein Society home page, read 2026-11-08). Because proteins sit inside cell biology, genetics and evolution, the field overlaps with those disciplines rather than standing apart from them.
Proteins are built from 20 amino acids joined into chains. The order of those amino acids, the sequence, is the starting point for everything else in the field (Nature Scitable, Protein Structure, read 2026-11-08).
How proteins are described: the four levels of structure
Scitable describes protein structure at four levels. The table restates those levels and pairs each with the kind of question it addresses in a lab. The pairing is this page’s editorial framing; the level descriptions come from the source.
| Level | What it is (Scitable) | Typical question at this level |
|---|---|---|
| Primary | The linear sequence of amino acids, linked by peptide bonds | What is the sequence, and where is it recorded? See NCBI Protein. |
| Secondary | Local folding into alpha helices and beta sheets, held by hydrogen bonds | Which regions form regular local patterns? |
| Tertiary | The three-dimensional shape of a single chain | What does one folded chain look like? See I-TASSER structure prediction. |
| Quaternary | The arrangement of several chains (subunits) into one complex | How do subunits assemble into a functional complex? |
How protein folding works in practice
According to Scitable, a protein’s final shape depends on its sequence, and hydrophobic groups tend to end up buried inside the folded chain. Cysteine side chains can form covalent bonds that stabilise a fold. In the crowded cytoplasm, proteins can misfold, and chaperones such as GroEL/GroES use ATP to help proteins reach their correct shape.
These points matter at the bench because a protein that has misfolded is not the protein the experiment was designed around. Treat folding as a variable to check, not a given.
Where structures are shared and how methods connect
The Protein Data Bank (PDB) is a global archive of three-dimensional structure data for large biological molecules, including proteins, DNA and RNA. The worldwide PDB (wwPDB) maintains a single free public archive, RCSB PDB is the US data center, and the archive grows by nearly 10% per year; PDB-IHM holds integrative or hybrid models (RCSB PDB, About, read 2026-11-08).
CASRAI covers individual methods in separate guides rather than repeating them here:
- Sequence records: NCBI Protein.
- Structure prediction: I-TASSER, and crowd-sourced structure puzzles in Foldit.
- Mass spectrometry: MS/MS spectrometry, with MaxQuant for data analysis and phosphoproteomics for modification studies.
- Separation by force: ultracentrifugation.
Common misunderstandings
- Sequence is not structure. Sequence determines the final shape, but the shape is a separate level of description (tertiary and quaternary) that has to be measured or predicted.
- One chain is not always the functional unit. The quaternary level exists because some proteins function as assemblies of subunits.
- A predicted structure is a model. The PDB archives structure data for molecules and also holds integrative models in PDB-IHM; check which kind of record you are using.
Frequently asked questions
What is protein science?
It is the field that studies protein structure, function, design and applications, including proteins’ roles in cell biology, genetics and evolution (Protein Society).
How many levels of protein structure are there?
Four: primary, secondary, tertiary and quaternary (Nature Scitable).
Where are experimentally determined protein structures archived?
In the Protein Data Bank, a free public archive maintained by the wwPDB, with RCSB PDB serving as the US data center.
Sources
- The Protein Society, home page: proteinsociety.org (read 2026-11-08).
- Nature Scitable, Protein Structure: nature.com/scitable (read 2026-11-08).
- RCSB PDB, About: rcsb.org/pages/about-us (read 2026-11-08).
