HBB (hemoglobin subunit beta; HGNC:4827, NCBI Gene ID 3043) is a human locus mapped to chromosome band 11p15.4 that encodes adult beta-globin polypeptide chain (146 aa; forms HbA alpha2-beta2 tetramer). HBB acts in erythrocyte cooperative oxygen transport, 2,3-BPG allostery & Bohr effect, together with HBG1 (A-Gamma Fetal Globin Gene), HBG2 (G-Gamma Fetal Globin Gene), and BCL11A (Fetal Hemoglobin Repressor Gene). Encodes the adult beta-globin subunit of hemoglobin A; mutated in sickle cell disease and beta-thalassemia.
Approved Symbol
HBB
Chromosomal Locus
11p15.4
Encoded Product
Adult beta-globin polypeptide chain (146 aa; forms HbA alpha2-beta2 tetramer)
p.Glu6Val causes Sickle Cell Disease; >300 alleles cause Beta-Thalassemia; treated by Lyfgenia lentiviral & Casgevy CRISPR therapies
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 3-exon canonical globin gene at the 3-prime end of the chromosome 11p15.4 beta-globin cluster, activated in adult erythroid precursors when the upstream Locus Control Region (LCR) loops away from HBG1/HBG2 to engage the HBB promoter via KLF1, GATA1, and LDB1.
Cellular & Tissue Expression Profile: Transcribed at extraordinary levels almost exclusively in late-stage bone marrow erythroblasts and reticulocytes, where HBB mRNA stability is maintained by 3-prime UTR alpha-complex ribonucleoproteins to constitute >96% of adult hemoglobin (HbA).
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Each 146-residue eight-helix (A–H) globin fold coordinates one ferrous (Fe2+) protoporphyrin IX heme ring via proximal His92 and pairs with two alpha-globin chains to form the allosteric alpha2-beta2 HbA tetramer, exhibiting sigmoidal oxygen binding regulated by pH/CO2 (Bohr effect, His146) and 2,3-bisphosphoglycerate.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Described as a molecular disease by Linus Pauling (1949), with the causative amino-acid change identified by Vernon Ingram (1956): the single missense mutation c.20A>T (p.Glu6Val / p.Glu7Val, HbS) replaces a hydrophilic glutamate with hydrophobic valine on the beta-chain surface, causing deoxygenated HbS to polymerize into rigid fibers that deform erythrocytes into sickled cells, while heterozygosity confers strong malaria resistance; over 300 splicing, nonsense, and promoter mutations reduce (beta+) or abolish (beta0) beta-globin synthesis in beta-thalassemia.
Therapeutic & Clinical Pharmacology: Treated curatively by FDA-approved autologous hematopoietic stem cell gene therapies: lovotibeglogene autotemcel (Lyfgenia, lentiviral delivery of anti-sickling HBB-AT87Q), betibeglogene autotemcel (Zynteglo, lentiviral betaA-T87Q for beta-thalassemia), exagamglogene autotemcel (Casgevy, CRISPR-Cas9 BCL11A enhancer editing), and investigational adenine base editors (BEAM-102) that directly convert HbS (GTG) into benign Makassar hemoglobin HbG-Makassar (GCG, p.Glu6Ala).