# Protein structure search Search large protein-structure databases with a query fold, then inspect ranked neighbors, coverage, scores, and alignments. [Open workflow](https://proteiniq.io/app/workflows/templates?template=protein-structure-search)[Contact sales](https://proteiniq.io/contact) ## More protein structure alignment workflows ## Tools for protein structure search Use these methods to prepare inputs, run the core analysis, inspect outputs, and validate the evidence described in this workflow. [![FoldSeek](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Ffoldseek.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### FoldSeek Search structure databases or compare and cluster uploaded protein structures](https://proteiniq.io/app/foldseek)[![USAlign](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fusalign.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### USAlign Align two protein structures and return TM-scores, RMSD, residue correspondence, and superposed coordinates](https://proteiniq.io/app/usalign)[![PDBFixer](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fpdb-fixer-featured.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### PDBFixer Repair common coordinate-file issues before structural comparison](https://proteiniq.io/app/pdb-fixer)[![PDB Download](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fpdb-download.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### PDB Download Retrieve experimental structures from the Protein Data Bank](https://proteiniq.io/app/pdb-download)[![AlphaFold Database Download](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Falphafold-database-download.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### AlphaFold Database Download Retrieve predicted protein structures from the AlphaFold Protein Structure Database](https://proteiniq.io/app/alphafold-database-download)[![PDB to FASTA converter](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fpdb-to-fasta.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### PDB to FASTA converter Extract protein sequences from coordinate files for sequence-aware review](https://proteiniq.io/app/pdb-to-fasta)[![HMMER](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fhmmer.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### HMMER Search profile hidden Markov models for independent sequence-level homology evidence](https://proteiniq.io/app/hmmer)[![MMseqs2](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fmmseqs2.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### MMseqs2 Search and cluster large protein sequence collections](https://proteiniq.io/app/mmseqs2)[![DSSP](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fdssp.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### DSSP Assign secondary structure and solvent accessibility from protein coordinates](https://proteiniq.io/app/dssp)[![MolProbity](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fmolprobity.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### MolProbity Check model geometry and steric quality before interpreting structural matches](https://proteiniq.io/app/molprobity)[![SASA calculator](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Fsasa-calculator.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### SASA calculator Calculate solvent-accessible surface area for matched structures](https://proteiniq.io/app/sasa-calculator)[![RMSD calculator](https://proteiniq.io/_next/image?url=%2Fimages%2Ftools%2Frmsd-calculator.webp&w=96&q=75&dpl=dpl_J8tu6aF3F41kEvMFgYtuMXes1ynJ) ### RMSD calculator Superpose comparison structures on one reference and report RMSD values](https://proteiniq.io/app/rmsd-calculator) ## What is protein structure search? Protein structure search is the process of querying a structural database with a three-dimensional protein model to find geometrically similar entries. FoldSeek represents local tertiary interactions with a structural alphabet, enabling fast candidate retrieval before detailed score, alignment, and biological review. Use it to find remote-homolog candidates, fold analogs, related domains, or structural neighbors when sequence search is insufficient. The query may be experimental or predicted, but chain choice, domain boundaries, missing residues, and model confidence affect retrieval. ProteinIQ runs FoldSeek database search directly against supported collections. Results retain identifiers, alignment statistics, [TM-score](https://proteiniq.io/guides/tm-score-vs-rmsd) and LDDT context, coverage, E-values, and files for detailed pairwise and biological review. ### When to use protein structure search Search by structure when the fold carries information that sequence search may miss: - A query domain needs remote-homolog candidates. - A predicted structure needs comparison with known folds. - A protein family needs structural neighbors for closer review. ### Strengths and limitations FoldSeek can search large structure collections quickly and return residue alignments alongside ranked matches. This lets a researcher separate a whole-chain fold match from a local domain or repeat match before investing in detailed superposition. The search cannot retrieve structures absent from the selected database. Query boundaries, missing residues and low-confidence predicted regions can change the result, while a similar fold alone cannot justify transferring molecular function or ancestry. ## How protein structure search works FoldSeek converts tertiary residue neighborhoods into a structural alphabet and applies sequence-search techniques. Database composition also matters: clustered predicted structures can reveal broad fold neighborhoods, while curated experimental entries may carry stronger ligand, assembly, and functional context. ## Applications of protein structure search A structural database search can find candidate remote homologs or analogs for a protein with weak sequence matches. The hits can help select templates, compare fold families or identify a model that resembles a known domain. For an uncertain predicted structure, matches to several unrelated folds can signal that only a small motif is driving retrieval. Inspect the aligned region and the query model's confidence before using any database annotation. ## How to run protein structure search online 1. **Prepare the query.** Select chain, domain, assembly, and state; review missing or low-confidence regions. 2. **Choose databases.** Set collections and thresholds for the needed sensitivity and result volume. 3. **Run database search.** Submit the query to [FoldSeek](https://proteiniq.io/app/foldseek) in database-search mode and preserve database selection, thresholds, warnings and failed inputs. 4. **Review matches.** Read rank, E-value, coverage, TM-score, LDDT, alignment, and length differences together. 5. **Validate candidates.** Confirm important hits with superposition, sequence evidence, annotations, and experiments. ## How to interpret protein structure search results Evaluate E-value, score, coverage, aligned length, TM-score, LDDT and sequence identity together. A low E-value for a short segment does not imply that two complete chains have the same fold. Structural similarity can prioritize a relationship to investigate, but it does not confirm common ancestry, biochemical activity or function. ## How protein structure search works FoldSeek performs the core structure search directly; downstream homology and function claims still require independent review. 1. **Prepare the query.** Choose the relevant chain, domain, assembly, and conformational state, and review missing or low-confidence regions. 2. **Choose databases.** Select structural databases and thresholds that match the intended sensitivity and result volume. 3. **Run FoldSeek.** Run FoldSeek while preserving database versions, search settings, warnings, and failed inputs. 4. **Review matches.** Inspect rank, E-value, coverage, TM-score, LDDT, residue alignment, and query–target length differences together. 5. **Validate candidates.** Confirm important candidates with detailed superposition, sequence evidence, curated annotations, and experiments when the claim requires them. ## Inputs and outputs Check formats before running, then inspect and download the result from every workflow step. ### Inputs #### Structure-analysis inputs `PDB``mmCIF``FASTA``TSV` One experimental or predicted protein structure in PDB or mmCIF format. ### Outputs #### Reviewable results `PDB``CSV``TSV``JSON``FILES` Ranked database hits, identifiers, E-values, coverage, TM-scores, LDDT values, alignments, and downloadable files. ## Frequently asked questions AI answers from our docs. 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