STh

STh is a small, heat-stable enterotoxin produced by enterotoxin-induced Escherichia coli (ETEC). STh is a 19-amino acid polypeptide containing three disulfide bridges^{[1, 2]}. STh stimulates an increase in intracellular cGMP levels by binding to intestinal guanylate cyclase C on the surface of small intestinal epithelial cells, leading to increased intestinal fluid secretion and electrolyte imbalance, thereby causing secretory diarrhea^[3]. STh is often used in vaccine development, but its low immunogenicity and small size present challenges, requiring the use of proteins or chemical binding to generate an immune response^[4].

References:
[1] Shimonishi Y, Hidaka Y, Koizumi M, et al. Mode of disulfide bond formation of a heat‐stable enterotoxin (STh) produced by a human strain of enterotoxigenic Escherichia coli[J]. FEBS letters, 1987, 215(1): 165-170.
[2] Dubreuil J D. Escherichia coli heat-stable enterotoxins[J]. The Comprehensive Sourcebook of Bacterial Protein Toxins; Elsevier: Amsterdam, The Netherlands, 2015: 874-910.
[3] Prasad H, Mathew J K K, Visweswariah S S. Receptor guanylyl cyclase C and cyclic GMP in health and disease: perspectives and therapeutic opportunities[J]. Frontiers in Endocrinology, 2022, 13: 911459.
[4] Wang H, Zhong Z, Luo Y, et al. Heat-stable enterotoxins of enterotoxigenic Escherichia coli and their impact on host immunity[J]. Toxins, 2019, 11(1): 24.

STh是一种由肠毒素诱发的大肠杆菌（ETEC）产生的小型耐热肠毒素，是一种含有19个氨基酸的多肽，包含三个二硫键桥^{[1, 2]}。STh通过与小肠上皮细胞表面的肠鸟苷酸环化酶C结合，刺激细胞内cGMP水平升高，导致肠道液体分泌增加和水电解质失衡，从而引起分泌性腹泻^[3]。STh常被用于疫苗开发，但其低免疫原性和体积小带来了挑战，需要携带蛋白或化学结合来产生免疫反应^[4]。