# A Proteoform-Resolved Atlas of Human Cardiac Histones

## TL;DR

This study creates a detailed map of histone proteins and their modifications in human heart tissue using advanced proteomics techniques.

## Contribution

The study introduces a streamlined top-down proteomics workflow to resolve histone proteoforms and their PTMs in native human cardiac tissue.

## Key findings

- A comprehensive cardiac histone proteoform atlas was assembled, revealing co-occurring PTM combinations.
- The workflow enables baseline separation of all core histone families and linker histone H1 in a single LC-MS run.
- Previously unobserved histone proteoforms were identified, providing insights into chromatin regulation in the heart.

## Abstract

Histones variant composition and post-translational modifications (PTMs) of core and linker histones jointly orchestrate chromatin architecture and tissue-specific gene regulation. However, capturing the full complexity of the “histone code” in native human tissues remains challenging. Here we present a human cardiac histone proteoform atlas—comprising intact histone variants with combinatorial PTMs—enabled by a streamlined top-down proteomics workflow. In a single one-dimensional reversed-phase liquid chromatography (LC)-mass spectrometry (MS) run, we achieve baseline separation of all four core histone families (H2A, H2B, H3, and H4) together with the linker histone H1 directly from human myocardium. Notably, this intact-protein analysis preserves the connectivity of co-occurring PTMs to individual histone molecules to reveal the combinatorial histone code, enabling proteoform-level quantification of histone-variant composition and PTM stoichiometry at the chromatographic scale. Targeted MS/MS directly resolves co-occurring PTM combinations and distinguishes highly homologous histone isoforms. Using this approach, we assemble the first comprehensive cardiac histone proteoform atlas and uncover previously unobserved histone proteoforms. More broadly, this top-down proteomics workflow provides a robust framework for proteoform-resolved analysis of histone variants and PTMs in complex biological systems.