TGM2

TGM2 Full Name

transglutaminase 2

TGM2 Introduction

Introduction
The TGM2 (transglutaminase 2) gene, also widely known as tissue transglutaminase (tTG) or G-alpha-h (Gαh), encodes a unique and multifunctional enzyme that stands at the crossroads of protein modification, cell signaling, and disease pathogenesis. As the most ubiquitously expressed member of the transglutaminase family, TGM2 is a protein of remarkable complexity, capable of catalyzing the crosslinking of proteins through calcium-dependent acyltransferase activity while also functioning as a G protein in transmembrane signaling independently of its enzymatic function. This bifunctional nature allows TGM2 to participate in an extraordinary range of biological processes, including apoptosis, cell adhesion, wound healing, extracellular matrix assembly, and angiogenesis. Its clinical significance is equally broad: TGM2 is the primary autoantigen in celiac disease, a key player in neurodegenerative disorders such as Huntington's disease, a promoter of cancer progression and chemoresistance, and an emerging therapeutic target in inflammatory bowel disease and fibrosis.

Figure 1. Strcuture of human transglutaminase 2.

Molecular Functions and Enzymatic Activities
TGM2 functions as a calcium-dependent acyltransferase that catalyzes the formation of covalent bonds between peptide-bound glutamine residues and various primary amines, including the ε-amino group of peptide-bound lysine residues, monoamines, and polyamines. This transamidation activity creates ε-(γ-glutamyl)lysine isopeptide crosslinks that stabilize protein polymers, contributing to the formation of detergent-insoluble scaffolds during apoptosis, extracellular matrix stabilization, and wound healing. The enzyme also exhibits several additional activities: it functions as a deamidase converting glutamine to glutamic acid (critical for generating immunogenic gluten peptides in celiac disease), as a GTPase/G protein (transducing signals from α1-adrenergic and thromboxane A2 receptors to phospholipase C), as a protein disulfide isomerase, and as a protein kinase. This functional versatility is tightly regulated: low calcium concentrations favor GTP-binding/G-protein activity, while elevated calcium (as occurs during apoptosis or cell stress) switches the enzyme to transamidation mode.

Role in Apoptosis and Cell Death
TGM2 plays a complex, context-dependent role in programmed cell death. During apoptosis, the enzyme is significantly upregulated and activated by the elevated intracellular calcium that characterizes dying cells. TGM2 then catalyzes extensive crosslinking of intracellular proteins, forming a detergent-insoluble scaffold that stabilizes apoptotic bodies and prevents the release of harmful intracellular contents such as lysosomal enzymes into surrounding tissues. This function has been proposed as a mechanism to limit inflammation and autoimmune responses during physiological cell turnover. Overexpression of TGM2 in neuroblastoma cells increases apoptosis rates, while antisense suppression reduces programmed cell death, establishing the enzyme as an active participant in the apoptotic program. However, Tgm2 knockout mice exhibit no major developmental abnormalities or defects in apoptosis induction, suggesting functional redundancy with other transglutaminase family members (particularly TGM1) and indicating that TGM2 is not an obligatory component of the core apoptotic machinery.

Alternate Names for TGM2

TGM2; transglutaminase 2; TG2; TGC; GNAH; HEL-S-45; G-ALPHA-h; protein-glutamine gamma-glutamyltransferase 2; TG(C); TGase C; TGase H; TGase-2; TGase-H; transglutaminase C; transglutaminase H; transglutaminase-2; tissue transglutaminase; epididymis secretory protein Li 45; protein-glutamine-gamma-glutamyltransferase; C polypeptide; protein-glutamine-gamma-glutamyltransferase; anti-TG2