Tf binding site classification

Reconstruct the transcription factor occupancy prediction step that classifies TF binding from footprint scores at motif sites

Summary

Classify transcription factor binding sites as bound or unbound by comparing footprint depletion scores at known motif locations across ATAC-seq conditions, using TOBIAS BINDetect to generate per-motif occupancy predictions and differential binding metrics. This skill bridges nucleosome-free chromatin signal analysis to discrete binding state estimates required for regulatory network interpretation.

When to use

You have aligned ATAC-seq BAM files, corrected Tn5 insertion bias and computed footprint scores (via TOBIAS ATACorrect and ScoreBigwig), a motif database in JASPAR or compatible format, and you need to assign occupancy states (bound/unbound) and confidence scores at specific TF binding sites to compare binding changes across experimental conditions (e.g., early embryo development timepoints, treatment vs. control).

When NOT to use

• Input is single-end ATAC-seq with very low read depth (<5M reads per sample); footprints will be too noisy to reliably detect binding occupancy.
• You are analyzing ChIP-seq or CUT&RUN data instead of ATAC-seq; this skill is specifically designed for footprint-based inference from transposase insertion patterns and will not apply to antibody-enriched chromatin.
• Motif database is not in a TOBIAS-compatible format (JASPAR, TRANSFAC, MEME); format conversion via TOBIAS FormatMotifs is required first.
• Footprint scores have not been corrected for Tn5 insertion bias; uncorrected scores will produce systematic false positives at sequence-biased sites unrelated to protein binding.

Inputs

• Aligned ATAC-seq BAM file(s) with corrected Tn5 cutsites
• Footprint score bigWig file(s) (output from TOBIAS ScoreBigwig)
• Motif database in JASPAR or TRANSFAC format (PWM file)
• Peak/open chromatin regions in BED format (optional, for restricting analysis scope)
• Sample metadata or condition labels (for comparing across treatments/timepoints)

Outputs

• BINDetect results table (TSV/CSV) with columns: motif_id, chrom, start, end, occupancy_state (bound/unbound), binding_probability, p_value, log2_fold_change (if multi-condition)
• Per-motif summary statistics (total sites called, fraction bound per condition)
• Visualization-ready BED files of bound TFBS coordinates
• Differential occupancy ranking (motifs with largest condition-specific changes)

How to apply

Load corrected footprint score bigWig files and scan a motif database (JASPAR-format PWMs) across the genome to identify candidate TF binding sites. Run TOBIAS BINDetect with footprint scores, motif match coordinates, and sample condition metadata to compute per-motif binding probabilities and occupancy estimates by comparing signal intensity at bound vs. flanking sequences. BINDetect applies a statistical model that distinguishes high footprint depletion (protein-bound) from baseline chromatin accessibility. Parse the BINDetect output table to extract occupancy predictions, binding probability scores, and condition-specific differential occupancy metrics. Format results as a structured CSV/TSV with columns for TF motif ID, genomic coordinates (chr:start-end), occupancy state assignment, confidence/p-value, and quantitative binding metrics per condition. The occupancy call relies on the underlying assumption that protein binding creates measurable Tn5 insertion depletion patterns detectable above noise.

Related tools

• TOBIAS BINDetect (Core tool for computing binding occupancy predictions from footprint scores and motif matches; outputs per-motif occupancy table and differential binding statistics) — https://github.com/loosolab/TOBIAS
• TOBIAS ScoreBigwig (Prerequisite: calculates footprint depletion scores from bias-corrected ATAC-seq cutsites, which BINDetect uses as input signal) — https://github.com/loosolab/TOBIAS
• TOBIAS ATACorrect (Prerequisite: corrects Tn5 insertion bias in ATAC-seq cutsite signal before footprint scoring) — https://github.com/loosolab/TOBIAS
• TOBIAS FormatMotifs (Utility to convert and standardize motif database formats (JASPAR, TRANSFAC, MEME) for use with BINDetect) — https://github.com/loosolab/TOBIAS
• TOBIAS PlotAggregate / PlotHeatmap (Visualization tools to aggregate footprint signals at predicted bound vs. unbound sites, for visual validation of occupancy calls) — https://github.com/loosolab/TOBIAS

Examples

TOBIAS BINDetect --signals corrected_footprints.bw --motifs jaspar_motifs.txt --genome genome.fa --peaks open_regions.bed --outdir bindetect_results --cores 8

Evaluation signals

• Output BINDetect table contains non-null entries for occupancy_state (bound/unbound) for >90% of motif sites; missing calls indicate convergence or filtration issues in the statistical model.
• Binding probability scores are bounded in [0, 1] and show distinct bimodal or left-skewed distribution (many unbound sites with low probability, fewer high-probability bound sites), consistent with sparse occupancy in open chromatin.
• Footprint visualization at predicted bound sites (via PlotAggregate) shows visible Tn5 insertion depletion centered on the motif, whereas unbound sites show uniform accessibility; mismatches suggest poor occupancy prediction.
• Differential occupancy metrics (log2_fold_change, p_value) are statistically meaningful and replicate across biological replicates; large variance between replicates suggests noise or inadequate bias correction.
• Top differentially occupied motifs correspond to known developmental regulators or condition-relevant factors (e.g., pluripotency factors in embryonic samples, cell-type-specific TFs in differentiated samples); random or implausible TF hits indicate overfitting or poor filtering.

Limitations

• TOBIAS footprinting assumes that protein binding creates detectable Tn5 insertion depletion; weak-binding or transient interactions may not produce sufficient signal to discriminate from noise, leading to false negatives in occupancy calling.
• The method relies on high-quality motif databases; incomplete, redundant, or low-specificity PWMs will produce spurious binding predictions and confound differential occupancy estimates.
• Originally developed for bulk ATAC-seq; application to single-cell ATAC-seq (scATAC-seq) requires generating pseudobulk BAM files from cell-type clusters, and quality depends critically on cell clustering and per-cell sequencing depth.
• Occupancy predictions are relative to footprint signal and do not directly measure binding kinetics or absolute occupancy fraction; quantitative interpretation requires comparison across conditions or cell types.
• No changelog or version tracking provided in the README; reproducibility across software versions or parameter tuning (BINDetect threshold settings) is not explicitly documented.

Evidence

• [readme] the local distribution of Tn5 insertions contains information about transcription factor binding due to the visible depletion of insertions around sites bound by protein - known as footprints: "the local distribution of Tn5 insertions contains information about transcription factor binding due to the visible depletion of insertions around sites bound by protein - known as footprints"
• [other] TOBIAS is a collection of command-line bioinformatics tools for performing footprinting analysis on ATAC-seq data, enabling detection of transcription factor occupancy through analysis of Tn5 insertion patterns: "TOBIAS is a collection of command-line bioinformatics tools for performing footprinting analysis on ATAC-seq data"
• [other] Run TOBIAS BINDetect with the footprint scores and motif matches as input, comparing signal intensity at motif sites across experimental conditions to discriminate bound from unbound sites.: "Run TOBIAS BINDetect with the footprint scores and motif matches as input, comparing signal intensity at motif sites across experimental conditions to discriminate bound from unbound sites"
• [other] Parse BINDetect output table containing per-motif occupancy predictions, binding probabilities, and differential occupancy scores across conditions.: "Parse BINDetect output table containing per-motif occupancy predictions, binding probabilities, and differential occupancy scores across conditions"
• [readme] Although TOBIAS was originally developed for bulk experiments, it can also be applied to single-cell resolution data. To do that, we recommend generating individual pseudobulk BAM files from scATAC-seq cell type clusters.: "Although TOBIAS was originally developed for bulk experiments, it can also be applied to single-cell resolution data. To do that, we recommend generating individual pseudobulk BAM files from"
• [readme] Estimation of bound/unbound transcription factor binding sites: "Estimation of bound/unbound transcription factor binding sites"