second high mobility group (HMG)-box found in the high mobility group protein B (HMGB) family
HMGB proteins are chromatin-associated nuclear proteins that act as architectural factors in nucleoprotein structures, which regulate DNA-dependent processes including transcription. In mammals, four family members are present: HMGB1, HMGB2, HMGB3 and HMGB4. They regulate the expression of a wide range of genes through architectural remodeling of the chromatin structure. HMGB1, also called high mobility group protein 1 (HMG-1), is a prototypical alarmin or damage-associated molecular pattern (DAMP) molecule when released from cells. It plays important roles in the regulation of a wide range of processes, including transcription, replication, DNA repair, and nucleosome formation, in the nucleus. It also plays multiple roles in regulating inflammation and responses to cell and tissue stress. HMGB2, also called high mobility group protein 2 (HMG-2), has been implicated in numerous cellular processes, including proliferation, differentiation, apoptosis, and tumor growth. It acts as a chromatin-associated nonhistone protein involved in transcriptional regulation and nucleic-acid-mediated innate immune responses in mammalian. It binds DNA to stabilize nucleosomes and promote transcription. HMGB3, also called high mobility group protein 2a (HMG-2a), or high mobility group protein 4 (HMG-4), is an X-linked member of HMGB family and functions as a universal sentinel for nucleic acid-mediated innate immune responses. HMGB3 has been implicated in the regulation of cellular proliferation and differentiation, as well as inflammatory response. HMGB4 is expressed by neuronal cells and affects the expression of genes involved in neural differentiation. It is a factor that regulates chromatin and expression of neuronal differentiation markers. The family also includes high mobility group protein B1 pseudogene 1 (HMGB1P1) and nuclear auto-antigen Sp-100. HMGB1P1, also called putative high mobility group protein B1-like 1 (HMGB1L1), or putative high mobility group protein 1-like 1 (HMG-1L1), is an HMG-box containing protein that binds preferentially single-stranded DNA and unwinds double-stranded DNA. Sp-100, also called nuclear dot-associated Sp100 protein, or speckled 100 kDa. It is a tumor suppressor that is a major constituent of the promyelocytic leukemia (PML) bodies, a subnuclear organelle involved in many physiological processes including cell growth, differentiation and apoptosis. Through the regulation of ETS1, Sp-100 may play a role in angiogenesis, controlling endothelial cell motility and invasion. It may also play roles in the regulation of telomeres lengthening, TP53-mediated transcription, FAS-mediated apoptosis, etc. In addition, the family includes Drosophila melanogaster high mobility group protein DSP1 (dDSP1) and similar proteins. dDSP1, also called protein dorsal switch 1, is a Drosophila HMG1 protein that binds preferentially single-stranded DNA and unwinds double-stranded DNA. It converts Dorsal and nuclear factor (NF)-kappa B from transcriptional activators to repressors. Members of the HMGB family contain two HMG-box domains. This model corresponds to the second one.
Jiyao W et al.(2023). "The conserved domain database in 2023.",