Heme is a widely known cofactor molecule in many enzymes like hemoglobin, cytochromes, and myoglobins. It is attached to these proteins covalently and classifies them as hemoproteins. In the last decade, a growing number of reports on the regulatory role of heme in various molecular and cellular processes uncovered the signaling role of heme. Here, heme binds transiently or with a low affinity to a variety of proteins and regulates their function. Inspite of the number of reports on its regulatory role, they are poorly defined at the structural level. Heme binds to these proteins through special amino acids called heme regulatory motifs (HRMs) such as cysteine-proline (CP), histidine and tyrosine. Studies conducted on CBS and the IL-36 cytokine family members during this project validated the heme-peptide knowledge at the protein level.